§<5. 274, 275. THE CRUSTACEA. 323 



The single stomato-gastrlc system consists of two short trunks which 

 extend from the brain in front, send several small filaments to the parts of 

 the mouth, and finally pass in front of the brain, — ending in a small gan- 

 glion. From this last, arises a single nerve, which passes under the brain 

 and extends along the oesophagus to the stomach, being, in its course, 

 sometimes enlarged like a ganglion. The double splanchnic system, on the 

 other hand, is composed of a double row of ganglia accompanying the 

 oesophagus, and connected, partly by the posterior border of the brain and 

 the single nerve, and partly by nervous branches. The filaments givea off 

 from these ganglia are distributed not only to the oesophagus, but also to 

 the salivary glands.*'' 



In the genus Lhnulus, there is observed, as a single splanchnic nerve, 

 only one nerve, having a ganglion and situated on the heart ;*^' while, with 

 Apus, the splanchnic nervous system is highly developed. The two 

 oesophageal commissures furnish, as with the Decapoda, two nerves which, 

 shortly after their origin, are connected by a transverse commissure. On 

 the oesophagus, they are blended into a single nerve, and send to this canal 

 numerous filaments. '■"' With the other inferior Crustacea, no splanchnic 

 nerves have as yet been observed. 



CHAPTER IV. 



ORGANS OF SENSE. 



§ 274. 



The sense of Touch is highly developed with Crustacea. Its seat is in 

 the multi-articulate antennae, situated on the head, or cephalic extremity, 

 which always contain large nerves arising directly from the brain. Often, 

 the masticatory organs have one or several pairs of tactile appendages ; and, 

 not unfrequently, several pairs of the feet neighboring the mouth, are 

 changed into tentacular, tactile organs, which play an important part in the 

 choice and prehension of food.*^* 



§275. 



As Olfactory organs, with the Crustacea, may undoubtedly be regarded 

 the two shallow excavations which, with the Macrura, and with Pagurus, 

 are situated in the basal joint of the two median antennae. Each of these 

 cavities communicates, externally, by a fissure-like opening, placed on the 

 upper surface of the joint, and usually fringed with fine bristles. Inter- 



S Brandt, Bemerk. &c. p. 34, Taf. in. fig. 6-9, Julus ; see his Verm. Schrift. 11. p. 47, Taf. IV. 



and in Muller's Arch. 1837, Taf. XH. fig. 7 g. 



(Scolopendra, Spirobolus, and Glomeris) ; also 4 Fan der Hoeven, loc. cit. p. 23. 



Newport, Philos. Trans. 1843, p. 246, PI. XI. fig. 5 Zaddnch, loc. cit. p. 36, Tab. IH. fig. 5. 



1, 2 (Julua). Trevirajius had already seen 1 The various differences of form of these tactile 



something of a single sympathetic system with organs belong rather to Zoology. 



