This instrument was designed for taking marine muds for analysis. The requirements were that it should raise a column of mud, from eight to sixteen inches long, and without appreciable disturbance, or contamination with metal. An instrument working on the same principle was used here by Mr. R. Macdonald, and was made in Oslo. The advantages of the present model are that, while small enough to be worked by hand, it is capable of taking larger samples, and from bottoms of very varying consistencies.

The Clyde Sea Area is in many ways an ideal ground for the investigation of the nutrient salts in the bottom deposits. The different lochs present a range of depth of water of from 0 to 200 metres: some parts have strong tidal currents up to five knots, while others are practically unaffected by the tide: some lochs have also been affected by the dumping of sewage and harbour sludge, and the effect of these can be examined. Conditions may also be compared in muds ranging from the loch heads to the almost open sea conditions at Ailsa Craig.

The inter-tidal habitats of the common limpet, Patella vulgata L,, have been investigated in relation to constant lunar tidal levels and tidal zones. The habitats of some common shore organisms which occur at approximately definite tidal levels or zones—and can therefore be used with discretion for zoning the habitats of Patella—are shown in a chart.

A study of the distribution of the common limpet on the shores of Devon and Cornwall has shown that limpets are absent or rare on those parts of the foreshore above high-water neaps which are subjected to prolonged periods of direct insolation. In the same locality limpets may be totally absent from the high-water region on cliff-faces or rocks facing southerly, but present on adjacent ones facing northerly or north-westerly. Strongly insolated habitats appear to be unviable as a result of the direct effect of the insolation on the animal, but the apparent deficiency of food in such habitats is probably also a limiting factor of importance.

The importance of the splash-line of any tidal level is emphasised. It is shown that in Devon and Cornwall the occurrence of low-water spring tides at about midday (and midnight) results in exposing to strong sunshine (and correlated factors) those regions of the shore above high-water neaps which face in a southerly direction. In other localities where high-water spring tides occur about midday, equivalent regions of the foreshore are not so strongly nor so persistently insolated as in the former.

Viable habitats may therefore occur in different regions on the shore in different localities or at different latitudes according to the local orientation of the substratum and local tidal phenomena.

Echinus esculentus, the larger common sea-urchin, occurs in the British Isles between tide-marks on rocky shores at about low-water spring-tide level in the localities given in Table I, page 292. It is, however, absent from apparently suitable foreshores in the Plymouth district, for reasons which are discussed in the present paper. Chadwick (1) states that “In Port Erin Bay it may be collected by hand on the beach, and on the ruined breakwater at low water of spring tides.” Elmhirst (2) records that “In this district (Millport) E. esculentus occurs abundantly between tide-marks in spring and early summer on rocky coasts; a few may be found at almost any other season. About February or early March a shoreward migration seems to set in, so that in suitable weather conditions some hundreds may be collected at springs between April and June. Then their abundance decreases until about November,from when until January it is at a minimum.”

The following investigations were carried out in order to test the validity of the oft-recurring statement to the effect that “burrowing organisms live under fresh-water conditions during low tide in estuaries.” This type of statement is usually made in respect to organisms which live in the sand or mud of estuaries in which, at low tide, a stream of fresh, water passes over the ground in which the organisms are buried.

I have not been able to find any references to show that work has ever been done on this subject with the idea of determining the actual salinity of the water held by such sand. Therefore I carried out the following experiments to try to find if data could be procured which would be sufficiently consistent to lead to any conclusions.

Measurements were made, throughout the year 1928, of the penetration of daylight into sea-water in the English Channel. One vacuum and two gas-filled potassium photo-electric cells were used below water. In all save the first series an efficient diffusing surface was used with the photometers so that the corrections for obliquity of illumination, necessary in our earlier work, were rendered almost negligible. From October onwards a more sensitive gas-filled cell was available for use, together with a more powerful amplifier and a more efficient insulation of the high-tension batteries; improvements in the switching of the photometers on and off were also incorporated.

The following conclusions have been reached :—

1. The conclusions put forward tentatively in 1928, concerning the agreement between the vacuum and gas-filled cells, have been substantiated in the main, although the vacuum photometer, which is relatively more sensitive to the blue end of the spectrum, generally indicated rather higher opacities.

2. There are no regular seasonal changes in the opacity of the water. A very high opacity occurred in the autumn of 1927, but this was not repeated in 1928.

3. On one occasion, in April 1928, an unusual degree of clearness of the water has been shown to have been associated with the influx of water of lesser salinity, from further out in the Channel. The clearness of the water at El in December, 1927, and September, 1928, is probably due to an influx of clearer water, though the salinity changes indicating this are not so well marked.

The present paper continues the account of my experiments ou the capacity of fishes to form conditioned responses towards definite stimuli under strict experimental control. No change has been made in the method of recording the results except in the section on auditory discrimination in the wrasse. This slight variation is explained in the appropriate place.

All the experiments described in this part belong to Section A of the previous paper (1), in which food is the unconditioned stimulus. The work which has been carried out in Section B will receive fuller treatment at a later date.

In continuation of the study of the vertical distribution of the pelagic young of Teleostean fishes, already reported on for 1924 and 1925 (1), a further fifteen stations were made with the two-metre stramin net in the daytime between April and September in 1926. The collections were made in a manner exactly similar to that for those of the previous years, hauls of ten minutes' duration being made almost always at six different depths with the net towed horizontally as near as possible at the same speed on each occasion. The Admiralty depth-recording instrument was used at every station, and the results for each haul are given in Figures 6 and 7 on pages 666 and 667, which show the graphic records of the path of the net through the water for each haul. (That for June 25th is not included, an unsatisfactory record being obtained on that day owing to the drum of the recorder not having been fully screwed down, see 4, p. 431.)

A Sacconereis “captured by the tow-net in the Firth of Clyde,” according to W. C. McIntosh (1908, p. 223, Fig. 5 f.), differs from any described female bud of Autolytus, or of its allied genera such as Myrianida or Proceræa of Ehlers, especially in respect to the shape and number of ovigerous sacs, which the animal carries on its ventral side. “It appears to be fully a quarter of an inch in length, and is readily discriminated by the absence of the single ventral egg-capsule, the ova being borne in eight conspicuous globular or pear-shaped sacs.”