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Pharaoh's Ant, Monomorium pharaonis (L.), is arrhenotokously parthenogenetic, conforming essentially to the pattern of reproduction characteristic of Hymenoptera generally. The female is diploid, 2n = 22, the male haploid, n = 11, in certain somatic cells and in the gonia, though polyploidy exists in some larval tissues. The 11 discrete chromosomes of the male cells comprise a single genome, in which are distinctive only one large clubbed chromosome and at least one of intermediate size. Spermatogenesis is characterized by a first abortive division and a second equational division, resulting in two spermatozoa being derived from each haploid spermatogonium. Spermateleosis is described in some detail. Certain peculiar features are discussed, viz. the cytoplasmic buds appearing during spermatogenesis; unequal second spermatocyte divisions; the single chromosome sometimes observed as lying apart from the other chromosomes during first spermatocyte metaphase; the division and grouping of polar body chromosomes. For reasons given, several recent conclusions of Whelden and Haskins (1953) regarding the cytology of ants are regarded as mistaken.
The exact age of the basalts and intercalated tuff-beds of Iceland is still uncertain. Palæontological dating relies almost solely on plant fossils the occurrence of which is known from many different localities in western Iceland. No plant fossils have hitherto been found in eastern Iceland. In summer 1952 an expedition set out from Scotland to search for plant fossils and lignite deposits intercalated in the East Icelandic Volcanic Series. Such deposits were found on the northern flank of the mountain Tungufell.
Macroscopical remains of plants were rare and badly preserved as compared with the finds in western Iceland, but a microscopical investigation of the lignite yielded 22 types of pollen and spores and 19 species and varieties of diatoms. The flora differs from that known of western Iceland; macroscopical remains and pollen of Abietineæ are abundant in western Icelandic sediments but are entirely absent in the Tungufell flora. The Tungufell flora appears to be younger than the fossil flora of western Iceland; however, the possibility that the difference between the Tungufell flora in East Iceland and the flora found in West Icelandic deposits is due to different ecological factors cannot be excluded. Many further investigations are required before this question may be satisfactorily answered.
In January 1956 a visit was made to North Ronaldshay, one of the Orkney Islands, to examine the rumen ciliate protozoa of the seaweed-fed native sheep. Rumen material from thirteen sheep was examined and the ciliate species identified. The numerical ratio of holotrich to oligotrich ciliates appeared to be much the same as in the hay-fed sheep's rumen; Isotriclia intestinalis Stein was, however, always absent. Certain experiments on the protozoan utilization of carbohydrates were carried out and the results compared with those of similar experiments on rumen liquor from hay-fed sheep. The holotrich ciliates of North Ronaldshay sheep were found to store amylopectin when the rumen liquor was incubated with laminarin, to a lesser extent when incubated with galactose and to be unaffected by mannose. These three results differ from previous experience with hay-fed sheep. No seaweed carbohydrate other than laminarin was utilized by the North Ronaldshay sheep holotrichs in vitro.
Structural changes induced in male auxocytes after formaldehyde feeding were analysed cytologically. In comparison with the effects of X-rays (on mature sperm) there is: (1) a high proportion of mosaics; (2) an excess of repeats and deficiencies; (3) a shortage of translocations, and (4) fewer breaks in the heterochromatic regions.
The very high frequency of mosaics and the low ratio of inter- to intrachromosomal changes may be explained by the delayed opening of potential breaks which tend to open simultaneously in the same chromosome but at different times in different chromosomes. The high number of “isochromatid” breaks (repeats) points to some connection with the reduplication cycle.
The shortage of “eu-heterochromatic” changes in which “heterochromatic” breaks in salivary gland analysis are scored, can be similarly explained by a difference in the time of opening of potential breaks in the two types of chromatin.
Initial non random distribution of breaks as well as the conditions of rejoining in premeiotic cells may also play some role.
Details of what occurs in the interval between the hatching of amœbulæ from the spores of the Proteus group of amœbæ to the attainment of the adult condition (4–6 months) not hitherto known are described. The method consists in removing mature adults to petri dishes 4 in. in diameter, containing a dilute inorganic fluid which causes sporulation. The subsequent development of the hatching amœbulaæ can be traced in situ by means of a 4·4 mm. water immersion lens, and is seen to consist of feeding and growth alternating with periods of encystment. The time spent in cysts greatly exceeds that of activity.
Some account of what takes place when cultures of the Proteus group, allowed to dry to a brownish dust, and then wetted, is given. Only in the case of A. proteus have the amœbulæ, which hatch out from the spores, been grown to maturity. It has been shown that the dried cultures used may comprise (1) spores, (2) cysts of varying size from which arise amœbulæ likewise varying in size.
The mineral base of the soils in Islay, Tiree, Coll and the Outer Hebrides is composed mainly of erosion products of Lewisian and Torridonian rocks, together with materials taken from solution in the sea biotically, and subsequently deposited in the form of shell-sand on the windward coasts. The soils composed for the most part of erosion products are acid, and those of marine products basic. Along transect lines at right angles to the coast there is in many places a wide range of soil conditions from calcareous sand to peat, in distances of about 1 kilometre.
The distribution of the Lumbricidæ, a group known to be affected by pH, available calcium content, and moisture content of the soil, is studied within this range in soil types. Seventeen species are involved, three of which are grouped (in numerical considerations) owing to taxonomic difficulties, and these are described in groups living in the main ecological zones of the soil habitat. Relationships are found between the abundance of those species and soil types.
The occurrence of earthworms in three different soil niches—open soil, in and under cow-pats, and under stones—is described, and niche preferences of the dominant species discussed.