118 THE ZOOLOGIST. 



" Communications " I., published last November by the " Millport 

 Marine Biological Station," contain a summary of a paper *' On Negative 

 Evidence regarding Influence of Nutrition on Sex," by J. F. Gemmill, 

 Lecturer on Embryology, University of Glasgow. 



It is well known that during a certain period in the early development 

 of most animals no difference, external or internal, can be detected between 

 the males and females. This undifferentiated stage is considered by some 

 to be a stage of sexual indifference more or less complete. There is a well- 

 known theory that during the period in question the future sex of indi- 

 viduals may be influenced by nutrition in such a way that a female bias is 

 given by rich and plentiful food, and a male bias by the opposite condition. 

 To test this hypothesis, Mr. Gemmill selected two molluscs for observation 

 — the Edible Mussel {Mytilus edulis), and the Common Limpet (Patella 

 vulgata). We give some extracts as regards the evidence afforded by the 

 first ; — 



" Mussels may be found in suitable places on the tidal zone at all levels' 

 from a little below high-water mark, downwards. They feed only when 

 immersed under water — that is to sav, when the tide is sufl&ciently far in to 

 cover them. Mussels placed high up on the tidal zone are thus able to feed 

 only intermittently, and during short periods. They grow slowly, and 

 remain small in size. The average weight of low-level Mussels on Keppel 

 Pier, Millport, is six or seven times greater than the average of high-level 

 specimens. These facts and similar facts regarding the fixed animals on 

 the tidal zone [e. g. Barnacles) point to comparative starvation of high-level 

 specimens as contrasted with those which occupy a lower position. 



"In the life-history of the Mussel there is first a free swimming stage, 

 then the larvae settle down and become permanently attached. At the time 

 when they fix themselves, and for a considerable period afterwards, their 

 sex, so far as I could make out by careful histological examination, is still 

 undifi'erentiated. During the first period of growth and differentiation of 

 sex, the young Mussels are subject to the different nutritive conditions in- 

 dicated above, according as they have placed themselves high up or low 

 down on the tidal zone. Nature thus supplies all the factors necessary for 

 an experiment, and works out the experiment herself. It only remains to 

 observe, in a large number of specimens taken from different localities, the 

 relative proportion of males and females at different levels. By comparing 

 these proportions we shall be able to tell whether richness or poorness of 

 nutrition, acting under the conditions above indicated, have had any 

 influence in determining sex in the young Mussel. A large number of 

 Mussels were accordingly examined. In order to avoid local peculiarities, 

 the batch of Mussels were taken from many different localities. 



" Results. — Out of the total number examiued, 49 per cent, were males, 



