A8TACU8 FLUVIATILI- 



azygos nerve, which passes forward and upward and n 

 the cerebral mass. I am inclined to think that this jait of 

 tin- a/\ ^os nerve forms a portion of a fine plexus of nervous 

 filaments which pass from the cerebral ganglia backward to 

 tin lining membrane of the carapace ; but the dissection of 

 these line fi laments, and the demonstration of their conti- 

 nuity, is a matter of no ordinary difficulty. 



the inii slim- is supplied by two nerves which aiise from 

 the last abdominal ganglion, and unite into a single trunk, 

 from which small branches are given off backward, and two 

 principal cues forward, which supply (he greater part of the 

 intestine. According to Brandt, the genitalia receive branches 

 of the fourth, tilth, and sixth thoracic ganglia. 



The only certainly kn<>\\ n organs of sense in AstacitS are 

 the eyes and the auditorv organs. The eyes are seated at 

 the extremities of the opiit haltnic peduncles, the integument 

 of the outer extremity of which becomes translucent over a 

 reniform space, and constitutes the cornea 1 membrane. This 

 membrane is divided into a great number of minute quadri- 

 lateral facets, each of which corresponds with the base of a 

 cr \stalline cone. 1 



The upper face of the trihedral, proximal, and largest 

 joint of the antennule presents an oval space, covered by a 

 broad brush of complex hairs having their points all directed 

 inward. On cutting these hairs away close to their bases, 

 however, it is seen that they cover an aperture, \\ider ahove 

 than belmv, and about one-sixte nth of an inch long. The 

 hairs are attaehed to the outer lip of this aperture, and some 

 are directed so as to lie within the inner lip, but the majority 

 r it. A o-ood-si/ed bristle passes with great ease into 

 this aperture, and if the inner and outer walls of the ha>al 

 joint of the antennule be now reino\ . d, and the soft parts 

 can-fully dissected away, the end of the bristle \\ill be E* n 

 to have pa>sed into a wide delicate BEO about one-twelfth of 

 an inch long, which is attached by a narrower neck round 

 the aperture, the lips of which are continuous with its walls. 

 The sac is filled with minute sandy particles, suspended in a 

 mucous, dirty-lookinir fluid, and when emptied of these con- 

 tents a band, consisting of several lines of very fine hairs, 

 like those which iruard the mouth of the sac, but more deli- 



' Mr. E. T. Nowton's rutvt'ul .1. -ription of the eye of the Lobster in Tht 

 Quarterly Journal of Micr< which I havi- referred 



, may be taken as a cruide to the studv of the minute structure of the ey 

 in the Cra'vflsh. 



