792 SUMMARY OF CURRENT RESEARCHES RELATING TO 



€. Crustacea. 



Physiology of Nervous System of Lobster.* — Mr. ( '. P 

 Marshall finds that there arc no motor or sensory roots in the lobster 

 analogous to those of tlio spinal nerves of vertebrates; though there 

 is no marked decussation of the ncrvc-ribrcs in the central nervous 

 system, nervous impulses readily travel across the ganglion ; each 

 ganglion is a reflex centre for the appendages which it supplies. 

 There is a distinct sense of touch which can bo exercised through the 

 thick cuticle in all parts, especially in the large claws. The 

 cerebrum is the scat of origin of inhibitory impulses and, conse- 

 quently reflex actions are much more marked when this mass is 

 separated from the rest of the nervous system. All the ganglia are 

 sensitive, i. c. respond to stimulation, formally nervous impulses 

 pass down the cord, but if this path be interrupted, they will pass 

 up it. 



Germinal Vesicle of Siphonostoma diplochoetos.f— M. E. Jourdan 

 describes the ova of Siphonostoma as measuring 130 /x, while the 

 germinal vesicle is 50 fx in diameter ; the latter contains all the 

 constituent parts of a cell-nucleus ; its nucleolus varies in form and 

 appearance, and appears to be altogether independent of the nucleus 

 itself. The principal nucleolus appears to be capable of producing 

 even when the ovum is in a state of repose, a certain number of 

 grains of a chromatic substance ; these detach themselves and migrate 

 into the substance of the nucleus to give rise to secondary nucleoli. J 



Influence of Rhizocephala on the External Sexual Characters 

 of their Host.§ — M. A. Giard gives on account of the influence of 

 Sacculina Fraissei on its host (Stenorhynchus phalangium). This new 

 species is entirely hidden in the cavity formed by the tail of the 

 crab and its sternal plastron ; its characters arc described, and it is 

 stated to be allied to S, corculum. Its female hosts have the four 

 pairs of ovigerous legs greatly reduced, and the males have much 

 shorter copulatory stylets. The secondary sexual characters of the 

 male are also affected, for the chelae do not extend beyond the head, 

 as they do in normal males. M. Giard thinks that a comparable set 

 of facts are only to be found in castrated vertebrates. Other parts of 

 Sacculinids may be found, on examination, to have the distinctive 

 sexual characters reduced and rendered less well marked. 



Nervous System of Peltogaster. || — M. Y. Delage says that, 

 havin<* obtained nearly 2000 examples of Pagurus, he founel that of 

 1651, 48 (or 1 in 35) were effected by the parasite Peltogaster; if medium 

 sized specimens alone are taken, 1 in 20 is found to be infested. 



Describing first the general arrangement of the organs, the author 



* Studies from the Biological Laboratories of the Owens College, i. (1886) 

 pp. 313-23. 



t Comptes Rendus, cii. (1886) pp. 1494-6. 



X "Molecules secondaires " is apparently a misprint for "nucleoles oocou- 

 daiivs." 



§ Coinptes Rendus, ciii. (1886) pp. SI 6. 



II Arch. Zool. Exper. et Gen , iv. (1886) pp, 17-36 (1 pi ). 



