Turner, Nervous System of Cvpris. 39 



2nd, in location it resembles the auditory organ of the higher 

 Crustacea [Alalacostraca). 



Olfactory Organs. — On the third joint of the antenna of all 

 the fresh-water Ostracoda, there exists a peculiar seta which all 

 writers have called an olfactory organ. As has been remarked 

 by other writers on this subject, this organ consists of the fol- 

 lowing three segments : basal piece, middle piece, end piece 

 [fig. 1 5]. In some cases the basal piece has been subdivided 

 into two pieces [fig. 17], while in others no middle piece can be 

 distinguished [fig. 14]. The nerve enters this organ through a 

 perforation in its base. Thence it extends along the axis of this 

 portion until it reaches the base of the middle-piece, where it 

 terminates in a small knob [fig. 15, 17]. In Cypris Jierricki 

 Turner this terminal knob is about three micromillimeters in 

 diameter. 



The usual width of this organ is about three micro-milli- 

 meters. However, in Cypria exculpta Fischer it is only about 

 two micromillimeters wide, while in Cypris herricki Turner it is 

 about eight eight micromillimeters wide. In length the organ 

 varies from about 85 micromillimeters in Cypris herricki 

 Turner to about 29 micromillimeters in Cypria ineqiiivalva 

 Turner. In the same genera the length of the organ varies 

 directly with the length of the body of the specimen — the 

 longer the body the longer the organ. In those genera in 

 which the swiming setae of the antenna are greatly developed 

 {Cyclocypris, Cypria^ this olfactory organ is relatively larger 

 than in those genera in which the natatory setaj of the antenna 

 are more feebly developed {Cypris, Cayidonci). 



In the same species the tip of this organ may be either 

 blunt or pointed. Indeed, on one antenna of a specimen the 

 apex of this organ may be blunt, while on the other the tip 

 may be pointed. 



The shape of this organ varies in different species. A 

 consultation of figures 12-15, 17-19 and 21-22 will give a bet- 

 ter idea of these various shapes than could any number of 

 words. 



