360 SECTIONAL TRANSACTIONS.— D. 



Three other films were shown at the same time : 



(i) By Mr. A. G. Lowndes. — Chirocephalns. 



(2) By Dr. P. D. F. Murray. — Beating and fibrillation in the chick 



embryo heart. 



(3) By Mr. C. H. Waddington. — Marine sand animals. 



Friday, September 11. 



Prof. C. M. Yonge. — Egg membranes and egg attachment in the Crustacea 



fio.o). 



The discovery that the integument of the Decapod Crustacea consists of 

 an inner chitin and an outer cuticle, the latter secreted by tegumental 

 glands, has made possible the elucidation of the nature of the membranes 

 surrounding the egg. The origin and nature of these has been the subject 

 of considerable controversy. 



As the egg descends the oviduct a layer of chitin, secreted by the epithelium, 

 is laid down around it. At this period the epithelial cells are greatly 

 elongated and resemble the chitinogenous epithelium at the time when this 

 is secreting chitin for the new integument. The outer membrane is 

 secreted by the tegumental glands which occur in great numbers in the 

 pleopods of the females. These resemble in every way the tegumental 

 glands which secrete the cuticle. The outer shell membrane which they 

 secrete, and which serves to bind the eggs to the pleopods of the female, 

 gives the same reactions as the cuticle. 



In Chirocephalus the eggs are coated by chitin secreted by the wall of the 

 oviduct, and later a rugose coat, giving the major reactions of cuticle, is 

 added by unicellular uterine glands. In both cases the primary significance 

 of the cuticular layer would appear to be that of protection, but in the 

 Decapoda it also serves for attachment. 



Prof. A. C. Hardy. — Plankton ecology and the hypothesis of Animal Ex- 

 clusion (10.30). 



A brief review is made of the former evidence of an inverse relationship 

 between the distribution of planktonic plants and animals, and in particular 

 that from the Discovery Expedition's South Georgia plankton survey of 

 1926-27 (Hardy and Gunther, 1935). The hypothesis of Animal Exclusion 

 and evidence in its support are discussed ; the exclusion of the animals from 

 the zones of plant concentration is considered to be one in a vertical rather 

 than a horizontal plane, and the inverse distribution seen in plan to be 

 secondarily produced by differing water movements at different levels. 



Dr. C. H. Mortimer. — -Parthenogenesis and bisexual reproduction in the 

 Cladocera (11.30). 



The alternation of parthenogenesis and bisexual reproduction in the 

 Cladocera and its causes were investigated under controlled cultural 

 conditions. Under optimum conditions parthenogenesis could be main- 

 tained over a considerable period (indefinitely ?) without signs of depression. 

 Various external factors — low temperature, lack of food, over-population 

 in the culture — could be made to cause the appearance of bisexual repro- 

 duction at will. The periodicity of the alternation in nature is therefore 



