232 BULLETIN OP THE BUREAU OF FISHERIES. 



nerves, a dorsal medio-lateral and a ventral or antero-lateral nerve of Huxley, which 

 send branches to a diffuse esophageal ganglion to be seen resting against the upper ante- 

 rior wall of the esophagus (pi. xxxiii) ; from this ganglion, moreover, a median bundle, 

 the anterior visceral or azygos nerve, runs up the wall of the stomach sac, to end in a 

 minute gastric ganglion lying between the origins of the anterior gastric muscles. A 

 smaller anterior median nerve also joins the esophageal ganglion to the brain. 



The stomato-gastric system thus consists of four peripheral ganglia, two of which 

 form a pair, and of peripheral nerves, which spring from them, in addition to a smaller 

 ganglion belonging to the labrum, to be mentioned presently. The dorsal or medio- 

 lateral nerve gives off two branches to the wall of the esophagus and bifurcates, a 

 dorsal division going to the esophageal gangUon and a ventral forming the labral 

 nerve, which has hitherto escaped notice. I have found that the two labral nerves end 

 in a small labral ganglion embedded in the fleshy mass of this organ; from it issue fibers 

 which presumably supply the sense organs of this part (see p. 237). The ventral nerve 

 gives off a small branch to the esophagus and divides, one section going to the eso- 

 phageal ganglion and the other passing to a plexus of fibers on the lower border of the 

 mouth; from this plexus a very diminutive median nerve is sent to the esophageal 

 ganglion. 



Allen has traced with great skiU the origin and course of the fibers in various nerves. 

 Many of these fibers, which have bipolar cells in their course and which terminate on 

 the walls of the esophagus, are possibly concerned with sensory cells. 



SENSE ORGANS. 



Special-sense organs, in so far as they are definitely known to exist in the lobster, 

 are (i) the eyes, and (2) the sensory hairs or setae, distributed over the body and 

 appendages, if we omit from this category those organs of equally wide distribution 

 which have the appearance of sensory buds and have received the general designation 

 of tegumental glands. The hairs embrace (a) tactile setae, which, though apparently 

 aimlessly scattered over the appendages, are really distributed in a definite manner, 

 including the setae of the statocysts, and (b) chemical setae, which aboimd on the 

 antennules and where for a long time they have been supposed to possess an olfactory 

 function, as well as on the mouth parts, to which a gustatory sense has been ascribed, 

 and indeed upon the surface of virtually the whole body, where experiment seems to 

 prove that chemical sense organs of some sort exist. 



EYES. 



At the time of hatching, the lobster possesses three visual organs, a me^ajuxyclo- 

 pean oceUus, a mere rudiment of the simple type of eye which proved useful to its ances- 

 tors and is still retained in the lower orders of Crustacea, and the paired lateral or 

 compound eyes. The latter, so conspicuous at all later stages of life, appear very early, 

 and at the close of the fourth week their black pigment can be detected as a dark crescent- 

 shaped line on either side of the head of the embryo. The eye is first disk shaped, then 



