872 RECORD OF CURRENT RESEARCHES RELATING TO 



goes to tliat segment of the body whicli in the larva bears the third 

 pair of hirval legs and in the adult the first pair of true legs. 

 But Dohru asks how these sacs are made out to be typical rather 

 than the generative cfecal sacs of which only four pairs are developed ; 

 in fact they cannot be in any sense regarded as typical, inas- 

 much as in some genera there are no ctecal sacs for the palp or the 

 ovigerous appendages ; while in others there are two pairs, and yet 

 again in others only one. Semper asserts that there are only six paired 

 ganglionic masses in the body, while Dohrn states there are eight. 



The statement of Cavanna that the egg-i>ouches arc found only on 

 the male is supported ; and the blood-corpuscles are stated to be 

 enormously large. Dr. Dohrn announces that he is preparing an 

 account of the Pycnogonida of the Gulf of Naples, 



S. Crustacea. 



Structure of the Nervous System of the Decapodous Crustacea.* 

 — In the summary of his results M. Yung enters into somewhat 

 greater detail than he did in the ' Comptes Rendus,f and we are able 

 to add one or two points of importance. 



The author points out that the absence of a differentiation of 

 myelin and of the axis-cylinder which is to be observed in the 

 central nervous system of Vertebrates, together with the form and 

 composition of the cells, brings the central nervous system of the 

 Crustacea into very close affinity with the sympathetic system of the 

 Vertebrata, the only difference between them being one of size. 



The thoracic ganglia of the Macrura have a similar structure to 

 the abdominal ganglia, and the slight differences between them may 

 be seen to be due to the concrescence of several ganglionic masses ; 

 this is best and most strikingly seen in the Brachyura, where there is 

 only a single thoracic ganglion. As already stated, the brain seems to 

 be formed of three ganglia, and it is possible, we may add, to distinguish 

 anterior, lateral, and posterior protuberances ; these are formed by a 

 comjjact medullary mass, which is finely dotted, and is divided into a 

 number of more or less cubical portions by fine lamella of connective 

 tissue, and distinguished histologically by being more deeply coloured 

 by osmic acid than is the rest of the nervous substance ; the medullary 

 mass is covered by a layer of nuclei, but it is not possible to dis- 

 tinguish any cellular investment ; the nerves of special sense have their 

 origin in the superficial cells of the protuberances, but it is not easy 

 to say exactly whence any particular nerve arises. 



It is interesting to observe that the studies of M. Yung confirm 

 the theoretical views, long ago propounded by M. Milne-Edwards, as 

 to the presence of three pairs of ganglia in the brain. 



Physiology of Muscle and Nerve in the Lobster.t— MM. Fredericq 

 and Vandevelde have contributed a paper on this subject to the Belgian 

 Academy. Their conclusions are as follows : — 



* ' Arcla. Zool. Exp.' (Lacaze-Duthiers), vii. (1878) p. 449. 



t See this Journal, ante, p. 419. 



X 'Bull. Acad. Eoy. Sci. Belgiaue,' xlvii. (1879) p. 477. 



