12 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



four fathoms under the surface, and when they do 

 occur it is only in ones and twos. Those prevailing 

 most on the surface in summer months (chiefly 

 Dexamine spinosa) almost entirely disappear during 

 winter, and are replaced by another (Atylus 

 Sicammerdamii ) that is seldom taken by the same 

 means, and is but sparingly met with round our 

 shores, whether by the net or dredge. When taken 

 by the tow-net, it is generally without any accom- 

 panying amphipodal species ; whereas in summer, 

 with few exceptions, a variety of different species 

 belonging to the same order may almost always be 

 met with. This periodical appearance of different 

 species seems to hold good even to a greater extent 

 with the smaller organisms. Ceratium tripos, one 

 of the Infusoria, was met with last summer in the 

 Firth of Clyde in great abundance from surface to 

 bottom ; but, by the time winter had set in, it had 

 wholly disappeared. The same may be said of 

 Noctihica miliaris. A few years ago it occurred in 

 excessive abundance in Millport Bay for a very 

 short time, but has not come under my notice 

 since. 



In regard to this section of the work, the staff 

 of the Millport Marine Branch Station purpose to 

 include the whole of the Invertebrate Fauna of the 

 Firth of Clyde, taken at various depths from the 

 surface to the bottom, whereby some knowledge 

 may be gained concerning the various depths at 

 which the food of fishes is attainable or most 

 abundant, and whether the food of the herring 

 may not be plentiful at depths hitherto unsuspected, 

 where the fish may resort when they leave shallower 

 water. 



The following list of the Amphipoda and Isopoda 

 taken by the surface-net after sunset, may be useful 

 to compare with deeper takes of the net during 

 day, and with those of the surface-net during sun- 

 light : 



