Archidistoma is a genus created for a species discovered and described briefly by Garstang in 1891 as A. aggregatum. It has been found at different times only in the Plymouth region, the original locality, attached to rock surfaces in a few feet of water. Recently, however, it has been found near Cape Hatteras on the eastern American coast (Van Name, 1945), suggesting either harbour to harbour transportation by ship bottom, or that its inconspicuous appearance has obscured a wide distribution.

This form is of considerable interest as it represents a type less specialized in zooid structure, nature of tadpole, and method of budding than any merosomatous ascidian except the diazonids. Diazonids are oviparous and have the simpler development and tadpole associated with small eggs, although there is a more elaborate branchial sac correlated with the relatively large size of the mature zooid.

Colony

The colony consists of a brownish tough matrix forming a thin encrustation on stones and shells, with individual zooids (a few millimetres long), partly embedded in the test but for the most part extending freely in clumps usually of three or four. Sand grains and round particles adhere to or become buried within the test, making this form the most inconspicuous of ascidians.

Structure of Zooid

The zooid is divisible into a thorax and a long slender abdomen (Fig. 1). There is no postabdomen, nor is there hypertrophy of the ventral test vessels, thereby segregating Archidistoma as a type from that of the synoicids (polyclinids) and the clavelinids respectively.

As is well known, the species Gammarus zaddachi, established by E. W. Sexton in 1912 on material from European brackish and fresh-water localities, has caused great confusion among zoologists, as the characteristics distinguishing it from various related species, particularly Gammarus locusta, G. duebeni and G. pulex, have been very frequently disregarded. This confusion still persists to-day—that is amply shown by the material received for the present investigations from various museums.

Diazona is represented in European waters only by Diazona violacea Savigny. It is a compound ascidian forming massive colonies of spectacular size and appearance. In many ways it is the most interesting of all ascidians, for in its adult structure it straddles two commonly accepted orders and in itself is a strong argument against such a division; it is the only oviparous and small egged compound ascidian, two features undoubtedly primitive; and its manner of budding is the simplest and probably is the basic type for the group as a whole. Only fragmentary descriptions of the morphology and reproduction exist, and a more or less complete account of the various stages of the life cycle may be of some value. The family Diazonidae includes, in addition to Diazona itself, the genera Tylobranchion of subantarctic regions, and Rhopalea of Mediterranean and northern waters. In its entirety Diazona appears to link with such divergent forms as Ciona on the one hand and Archidistoma on the other. The fact that Diazona is obtained by dredging in relatively swift offshore waters and lives poorly in an aquarium probably accounts for the existing unsatisfactory state of knowledge of most of its phases. Most of what is known concerns asexual reproduction; and attention has been given, at various times, primarily to the process of regeneration, rather than bud formation, for example by Della Valle (1884), Caullery (1914), Oka (1906) under the name Aphanobranchion, and by Salfi (1926).

The material of the present account was collected at various times in the Plymouth area from the Mewstone and Eddystone grounds.

The production, longevity, growth, regeneration and reproduction of Laminaria saccharina (L.) Lamour. on the Devon and Argyll coasts are described.

Bathymetric zone and habitat control the fertility and longevity of the gametophyte and consequently the production of the sporophyte. Sporophytes develop at the higher levels during the winter, early spring, late summer and autumn, and at the lower levels during spring, summer and autumn.

Longevity of the sporophyte depends on season of germination, bathymetric zone and habitat. Winter sporophytes rarely persist to maturity. Spring sporophytes form the bulk of all L. saccharina populations except on very sheltered coasts in the sublittoral zone where summer sporophytes may be equally numerous. On the British coast the life-span of a L. saccharina sporophyte does not exceed 3 years.

Pycnoclavella aurilucens was recorded and briefly described by Garstang in 1891 from a limited locality in the Plymouth area, and has not been found with certainty of identification from any other region. There has been a tendency to subordinate it as a species of Clavelina, but the dissimilarities are greater even than the original description implies and this procedure is not justified. The genus is accordingly retained, and a more detailed account of the colony, with the first description of the tadpole larva and process of budding, is presented.

Dr T. B. Reynoldson of the Department of Zoology, University College of North Wales, Bangor, found some large enchytraeids on the shores of the Menai Straits. He suspected that it was an undescribed, or at least a rare and interesting species, and kindly sent six specimens to me for further study. I find that the specimens are indeed to be ascribed to a new species, which is here named Lumbricillus reynoldsoni, in recognition of the finder's prominent work on the ecology of Lumbricillus lineatus Mull, and Enchytraeus albidus Henle.

A survey was made during 1946 covering the Amphipoda of the south end of the Isle of Man from an ecological aspect. The object was to revise the records of the area and to obtain additional information about the habitats of the species found.

The area in which the survey took place was within a radius of 10 miles from Port Erin.

Various sorts of gear were used for collection offshore and it is concluded that the fine-meshed dredge is the most useful instrument for collecting amphipods.

A systematic treatment of the species found includes a summary of records regarding habitat for each species.

It is suggested that the Amphipoda may be of greater economic importance than has previously been realized.

A discussion of offshore, intertidal, and brackish-water habitats includes lists of the more important species obtained grouped according to type of ground and zonation with regard to tidal level and salinity. The importance of offshore species is assessed on a basis of the average number of individuals collected per haul.

Comparison of the zonation of littoral and estuarine species with that known from other areas reveals a general agreement.

The existence of more than one form of several species of the genus Gammarus is discussed and it is suggested that they are in an active state of evolution.

I am indebted to Prof. J. H. Orton for encouragement and discussion, and to Mr G. M. Spooner for allowing me to read a proof of his recent paper.

The 1947 records of the seasonal abundance of the pelagic young stages of teleosteans in the plankton of Plymouth off-shore waters are a continuation of the series of observations made by Mr F. S. Russell (1930–47). The form of the previous reports is retained. The dates on which collections were made are given in Table I, and the monthly average catches of young fish in Table II. The fortnightly averages of all young fish less clupeids are shown in Fig. I, together with the corresponding curve for the period 1930–34.

The morphology and reproduction of Trichodina branchicola n.sp. are described. Its total diameter is 30–54μ, and its height is 20–36μ,; the diameter of the striated ring is 19–33μ, and the diameter of the denticulate ring 10–20μ. There are 20–26 denticles in the ring, with 6–8 striations to each denticle. The denticles measure 1·5–2μ, in thickness, 3·5μ in length, each with a broad outer hook 2·3μ long and an inner ray 3·2μ long. The aboral cilia are fused at their base to form a complete membranelle.

This organism is found on the gills of the following marine fishes at Plymouth: Ciliata mustela, Gaidopsaurus tricirratus, Cottus bubalis, Spinachia spinachia, Blennius pholis, B. guttorugine, Trigla lucerna and Pleuronectes platessa.

The genus Vauchomia Mueller 1938 is regarded as a synonym of Trichodina.

A description is given of characters which allow the larval stages of Balanus balanoides, B. crenatus and Verruca stroemia to be identified rapidly.

It is emphasized that the characters used in this method of identification are only valid for these three species inter se, further work on similar lines for other species may reveal difficulties not apparent in the present scheme.

Experiments with larvae of Ophelia bicornis Savigny have shown that they metamorphose most readily in sand from their natural habitat and with hesitancy or not at all in sands from other sources. Their natural sand consists largely of smooth rounded grains of quartz, very uniform in size; sands of smaller and more angular grains are unfavourable to settlement and metamorphosis. It appears that size and shape of the sand grains, or perhaps, more likely, the sizes and shapes of the interstices among the grains, perceived probably by the tactile sense, is the main stimulus to metamorphosis. Chemical substances dissolving out of the sands do not seem to be responsible for this.

There is a period of time, amounting under favourable conditions to several weeks, during which an Ophelia larva is able to settle and metamorphose as soon as it comes into contact with a substratum suitable for adult life.

The ability of the larvae to distinguish bottom deposits suitable for adult life from those which are unsuitable must be of great advantage to the species in maintaining normal distribution and in conserving larvae.

In the course of some 4 years′ work on the biology of fouling organisms, observations have been made on aspects of the general biology of Balanus balanoides, B. crenatus and Verruca stroemia.

Observations on the state of development of the ova within the mantle cavity of B. balanoides and of the occurrence of the larvae in the plankton indicate that hatching takes place during the first fortnight in March, that the later-stage nauplii are abundant during the second half of that month and that the cyprid larvae may become abundant during April. The larval sequence is not always completed successfully; conditions which seem inimical are discussed.

Factors which seem to be of importance in affecting settlement of B. balanoides are discussed. The presence of other organisms is an adverse factor, though the potency of this factor is probably not the same for all organisms; the presence of slime can prevent settlement and, though evidence can be quoted in support of heavier settlement on shaded surfaces, it is emphasized that the operation of other factors may have brought about this result. The proportion of the tidal cycle during which current speeds are not too high to prevent settlement seems likely to be important.

Provided that other conditions are favourable B. balanoides settles readily on surfaces continuously immersed and individuals which settle under these conditions grow more rapidly, at least for the first few months after settlement, than their contemporaries on the shore.

The larvae of B. crenatus appear in the plankton rather earlier than those of B. balanoides, but the time taken to complete the larval sequence from the 1st stage nauplius to the cyprid is roughly the same as that for the latter species, namely 1 month. In B. crenatus, however, hatching is not limited to a short period during March but continues at intervals through the summer. There are indications that the successful completion of the larval sequence of this species is less affected by an abundance of phytoplankton than is that of B. balanoides.

Settlement of B. crenatus is periodic and individuals which settle early in the spring can attain practically their full size (28–30 mm. basal length) during the same season. Growth during the summer takes place at average rates which vary from 0·1 to 0·2 mm. increase in basal length per day. Growth is negligible during the winter months.

Specimens of B. crenatus which settle early in April contain developing ova by the beginning of July, so that spring-settled forms can produce larvae which themselves may settle before the end of the summer.

Observations on Verruca stroemia have been limited to the occurrence of the larvae in the plankton. Like those of Balanus crenatus, the larvae of Verruca stroemia are present at intervals through the summer. Early-stage nauplii of this species may dominate the plankton early in the year, but no correspondingly heavy hauls of later-stage nauplii have been recorded. Possible explanations of this discrepancy are discussed. The cyprid never occurs in any numbers in surface hauls.

Incidental observations on the planktonic occurrence of the nauplii of Sacculina (probably S. carcini) and of Peltogaster paguri are given.

Details are given of the abundance of all Cirripede larvae in the plankton for the years 1944–47 which emphasize the extent of variation that can occur from year to year.

In The Times of 31 March 1884, it was announced that a meeting would be held that day in the rooms of the Royal Society for founding a society having for its purpose ‘the establishment and maintenance of a well-equipped laboratory at a suitable point on the English coast, similar to, if not quite so extensive as, Dr Dohrn's Zoological Station at Naples’ (M.B.A., 1887a). With Prof. T. H. Huxley in the chair a gathering of distinguished gentlemen gave reasons why such a laboratory should be built. All stressed what its value would be from the purely scientific viewpoint, and all were agreed that both by fundamental research and by more direct investigations on our food fishes, knowledge of economic import would be gained. The last speaker, Mr George J. Romanes, said that there was one function of the proposed laboratory which had not received the attention it appeared to deserve; he meant the investigation of invertebrate physiology. ‘In the invertebrate forms of life’, he said, ‘we saw life in its simplest shape, and in the shape which best admitted of observation and experiment, with the view of throwing light upon most of the great questions relating to the processes of life’ (M.B.A., 1887b).

The action of the following compounds on homogenates of the adductor muscles of Saxostrea commercialis was studied: urethane, phenyl urethane, chloral hydrate, salicylic acid, morphine, caffeine, barbitone, benzoic acid, salicylamide and benzamide.

It was found that, except for 0·05 M urethane, the endogenous oxygen consumption was reduced by all these compounds when present in concentrations ranging from o·001 to 0·05M. The oxidation of succinic acid was partially inhibited by these substances.

These findings are discussed in relation to similar studies on other tissues.