MisceUa neous. 219 



to distinguish, sinct,- tht>y have distinctly characterized relations and 

 attributions. 



The do termination of the homologous parts of the different ganglia 

 has led to the recognition of a new arrangement equally curious and 

 unexpected, which will, I hope, interest jihysiologists. 



It is well known thai in the neighbourhood of the external oritice 

 of respiration there is to be found, at the extremity of a large pallial 

 nerve, a ganglion of moderate size, to which one was tempted to give 

 the name of rts^iirdtur;/ (jcDu/Iion, in consequence of the functions 

 which its position caused to be ascribed to it. Now, by subjecting 

 this ganglion to microscopic observation, both directly and after 

 chemico-histological preparation (in a word, by analyzing it), we find 

 that it is formed of an accumulation of nervous corpuscles, almost 

 all unipolar, in the midst of which is immersed an actual ca^cal pro- 

 cess of the skin. This arrangement shows that here the outer limits 

 of the body, by a sort of invagination, become approximated as 

 closely as possible to a nervous centre and to the deep-seated 

 elements characteristic of the centres. 



Thus, from the study of the minute structure of the nervous 

 centres of the aquatic pulmonate Gasteropoda we may deduce : — 



1. That in these animals, as in higher creatures, there exist 

 regions or lobes the histological constitution and the connexions of 

 which establish for them distinct, special, and localized attributions. 



2. That the nerves of special sensibility originate from the pos- 

 terior part, whilst the nerves of motion have their origin upon the 

 most anterior ganglion. 



3. That we must recognize in the supposed respiratory ganglio^ 

 not a nervous centre or true ganglion, but a new special organ 

 produced by the invagination of the skin in the midst of a mass of 

 ganglionic corpuscles. — Comjates Renclus, July 17, 1871, tome Ixxiii. 

 p. 161. 



Further Observations on the Development of the Crayfish. 



By S. CnANTRAN. 



My recent experiments have confirmed the facts noted by me last 

 year*, especially with regard to the period of the life of the young 

 crayfish beneath the abdomen of the mother. I have observed that 

 not only do they feed upon the pellicle of the eggs and on the cara- 

 pace shed in their first moult, but the stronger ones eat those indi- 

 viduals whose development is rendered difiicult by their agglomeration 

 and which cannot moult. The facilitation of this moult is probably 

 one of the causes of the mother constantly agitating her false legs 

 during the two or three days preceding exclusion ; to these the young 

 crayfish are suspended. Those which, in moulting, break their 

 limbs, are also devoured by their companions. Thus the crayfish, 

 when they are ten days old, eat each other ; and this is the case also 



* See Ann. & Mag. N. H. ser. 4. vol vi. p. 265. 



