222 THE ANATOMY OF INVERTEBRATED ANIMALS. 



genous products of the waste of the tissues from the blood 

 is effected in Arthropods requires further elucidation. In 

 many, however, such products, notably uric acid, have been 

 found to abound in the corpus adiposum — a cellular mass 

 which lies in the walls of, and more or less fills, the peri- 

 visceral cavity — and in the Malpighian glands. In the latter 

 case, they are conveyed out of the body by the intestine. 



The nervous system consists primitively of a pair of gan- 

 glia for each somite, but the number of ganglia discoverable 

 in the adult depends on the extent to which these primitive 

 ganglia coalesce. There is usually, if not always, a well- 

 developed system of ganglionated visceral nerves, connected 

 with the cerebral ganglia and distributed to the gullet and 

 stomach. 



Eyes are usually present ; and, when they exist, they are 

 almost always situated in the head and are connected with 

 the cerebral ganglia. Among the Crustacea, however, tti- 

 phausia has eyes in some of the thoracic limbs, and in some 

 abdominal somites. The eyes may be simple or compound. 

 In the latter case there are, in correspondence with the num- 

 ber of parts into which the transparent corneal continuation 

 of the chitinous cuticula over the eye is divided, a number 

 of elongated bodies which lie between the outer surface of 

 the ganglionic expansion of the optic nerve and the inner 

 face of the cornea. These bodies consist of two parts: an 

 external transparent crystalline cone and an internal pris- 

 matic rod. The broad end of the cone is external, and is ap- 

 plied to the inner surface of the corneal facet; its narrow 

 end is continuous with the outer extremity of the prismatic 

 rod, which, by its inner end, is connected with the ultimate 

 ramifications of the optic nerve. Each of these crystalline 

 cones and prismatic rods is separated from the rest by a pig- 

 mented sheath. 1 



Distinct auditory organs have been observed in Crus- 

 taceans and Insects. They are not exclusively confined to 

 the head. In the opossum shrimp (My sis), for example, they 

 are placed in the appendages of the last somite of the ab- 

 domen. And, in Insects, the only organs to which the audi- 

 tory function can be certainly assigned are situated in the 

 thorax or in the legs. 



1 Leydig, " Das Auge der Gliederthiere,' 1 1864. Schulze, " Untersuch- 

 ungen," 1868. Mr. E. T. Newton has given a very good account of the struct- 

 ure of the eye of the lobster, accompanied by full references to the literature 

 of the subject, in the Quarterly Journal of Microscopical Seience for 1875. 



