$$ 274, 275. THE CRUSTACEA. 323 
The single stomato-gastric 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 wsophagus 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 
esophagus, and connected, partly by the posterior border of the brain and 
the singie nerve, and partly by nervous branches. The filaments given off 
from these ganglia are distributed not only to the cesophagus, but also to 
the salivary glands. 
In the genus Limulus, 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 
cesophageal commissures furnish, as with the Decapoda, two nerves which, 
shortly after their origin, are connected by a transverse commissure. On 
the cesophagus, 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. Lach 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- 
8 Brandt, Bemerk. &c. p. 34, Taf. IIL. fig. 6-9, Julus; see his Verm. Schrift. If. p. 47, Taf. IV. 
and in Muller’s Arch. Lees peal 7 B ey ee eee 
‘Scolopendra, Spirobolus, and Glomeris) ; also an der Hoeven, loc. cit. p. 23. 
Caliah, Philos Trans. 1843, p. 246, Pl. XI. fig. 5 Zaddach, loc. cit. p. 36, Tab. III. fig. 5. 
4, 2 (Julus). Treviranus had already seen 1 The various differences of form of these tactile 
somthing of a single sympathetic system with organs belong rather to Zodlogy. 
