SECTIONAL TRANSACTIONS.— D. 331 



water is slightly more acid (or less alkaline) than the surface. When the pH of the 

 aquarium water is uniform these movements cease. Aggregations of Colpidium and 

 Paramecium in cultures can be completely controlled by varying slightly the pH of 

 the culture. Slight changes in the pH of the culture also materially affect the powers 

 of these ciliates to ingest food. If a layer of distilled water be placed over some 

 culture fluid containing Paramecium in a test tube the Paramedian can be made to 

 rise into the distilled water or not by slightly varying the pH of the culture fluid. 

 If the pH of the culture fluid is adjusted so that the Paramecium are just able to 

 rise from it into the distilled water, they can be prevented from rising bv adding a 

 trace of Mg (1 in 100,000) to the distilled water. The pH of the culture fluid controls 

 this sensitivity to Mg and other kations. 



Prof. W. Garstang. — The Origin of Appendicular ians. 



Mr. J. R. Bruce. — Physical Factors on the Sandy Beach. 



The complexity of the distributional and other responses of shore-living organisms 

 points to their being the integrated result of many variable factors operating inde- 

 pendently. The measurement and recording of such factors is an essential preliminary 

 to a general ecological survey of the littoral fauna and flora. 



No region of the seashore — possibly no other region of the entire biosphere — is 

 subject to such frequent and far-reaching fluctuations as the sandy beach, and in this 

 paper an attempt is made to indicate the nature and range of some of the more 

 important factors operative in that region. 



The dominant influence is undoubtedly the tidal rhythm, every other factor — 

 temperature, salinity, oxygen-pressure, hydrogen-ion concentration, &c. — undergoing 

 a semidiurnal change with the advance and return of the tidal flow. The effects of 

 this major rhythm may be profoundly modified, however, by variable factors of 

 longer period, both daily and seasonal, including meteorological changes, and the 

 composition of the sea-water itself. In addition to these, numerous non-periodic 

 factors are to be reckoned with, including the effect of fresh-water draining from the 

 land, variations of grain-size or ' grade,' with corresponding differences in retentive 

 and adsorptive capacity, lithological differences in the sand-substance, and the 

 varying proportion of organic detritus due, in most cases, to the very organisms whose 

 physical environment we are studying. 



Mr. C. F. Hickling. — Dogfish in the Faroe- Shetland Channel. 



In the Faroe-Shetland Channel it was noticed that, in very deep water, all specimens 

 of the dogfish Acanthias vulgaris taken in the trawl were males, whereas in shallow 

 water females predominated. 



Now the liver in the female dogfish is much larger, proportionately, than that of 

 the male, and is also proportionately lighter ; it must therefore tend to act as an 

 organ of flotation, so that a female dogfish will require less effort to maintain its level 

 in the water than a male. If one can assume that, in the dogfish, there are periods 

 of diminished activity, such as after heavy feeding, the males will tend to sink to the 

 bottom more readily than the females, and will therefore tend to predominate in hauls 

 made in deeper water. This theory accords with the fact that pregnant females, 

 which are heavy owing to the large eggs and developing young, are found to a much 

 greater extent in deeper than in shallower water. 



It is suggested that in bathypelagic fish, such as the dogfish, the varying sex-ratios 

 found at different depths are due, in part, to a mechanical separation due to differences 

 in specific gravity. 



Prof. A. E. Cameron. — The Experimented Removal of Grabeis Organ in 

 Tabanid Fly Larvcc. 

 By reason of its comparatively large size, Graber's organ lends itself admirably 

 to experimental treatment, and as its true function has not been definitely determined 

 it was thought that any modification in the behaviour of the larva following the extir- 

 pation of the organ might shed some light on this question. The chitinous, cystoid, 

 pyriform organ is invariably found in the eighth abdominal segment, and contains a 

 variable number of black, pedunculated, globular bodies. It possesses its own system 



