618 CLASS X. 



lobster. In the hermit-crab (Pagurus) there are, besides the cephalic 

 ganglion, only six ganglia, but the form of the nervous system is 

 in other respects the same 1 . 



The nervous system existing especially for the organic life, 

 which we have already noticed in insects and spiders, is not want- 

 ing in the crustaceans also, however it still in many families 

 remains for the most part or entirely unknown. It has been 

 especially investigated by BRANDT in some Decapods, Stomapods 

 and Oniscides. In crays and in Squilla it consists of a single 

 portion and two lateral portions. The single portion arises at the 

 posterior margin of the cerebral ganglion, and has no nervous 

 ganglion that lies in front of the brain as in insects ; the lateral 

 portions arise from the oesophageal band that connects the cerebral 

 ganglion with the succeeding ganglionic cord. Distinct ganglia are 

 not present at the origin of the lateral portions, but appear to 

 be fused with the oesophageal band, which indicates a swelling at 

 the point of origin of these lateral nerves. The system of nerves 

 spreads itself over the stomach, presents here one or two ganglia, 

 and finally divides into two branches which are distributed to the 

 liver. In Porcellio BRANDT found no single portion of this system, 

 but only two small lateral swellings, situated behind the cerebral 

 ganglion and connected to it by two thin filaments, which send fine 

 branches backwards to the stomach 2 . 



In most crustaceans, common feeling on account of the hardness 

 of the covering cannot be otherwise than very small. The antennae, 

 which are often much developed and four in number, are wanting 

 only in few, and, like the whiskers in mammals, may serve for a fine 

 sense of touch even in the dark. In like manner, probably, the 

 jointed filaments of the cirripedia, and the filaments on the foot- 

 jaws of the decapods and other appendages of the body, may serve 

 for touch in many species. A special organ for taste is not known, 

 but the seat of this sense appears to be in the commencement of the 

 ossophagus 3 . 



1 SWAMMERDAM Bijbel der Ncduur. bl. 204206, Tab. xi. fig. ix. ; comp. also 

 OWEN, Catalogue of the physiol. Series of the Museum of the Coll. of Surgeons, iv. 

 pp. 16, 17, who in other species of the same genus found only four ganglia besides the 

 cerebral ganglion. 



3 Comp. BRANDT in his BemerTcungen uber die Eingeweidenerven der Evertebraten, 

 cited above (p. 279). 



3 According to MILNE EDWARDS, who appeals to his observations made with 



