472 



CEPHALOPODA. 



Fig. 216. 



to its posterior part, a minute otolithe (1, 2, 3), a calcareous 

 body of variable shape in different genera, the oscillations of 

 which doubtless increase the impulses whereupon the production 

 of sound depends. 



Such is the simplest form of an ear ; and if the reader will com- 

 pare the organ above described with that possessed by the highest 

 Articulata, as, for example, the lobster ($ 380), the similarity of 

 the arrangement will be at once manifest. 



(513.) All the CEPHALOPODA are dio3cious, and the structure 

 of the sexual organs both of the males and females is remarkable, 

 inasmuch as it is peculiar to the class. 



In the females, the ovarian receptacle is lodged at the bottom of 

 the visceral sac (Jig. 211, p, p), enclosed in a distinct peritoneal 

 pouch. The ovary itself is a large bag, the walls of which are 

 tolerably thick ; 

 and, on opening 

 it, it is found to 

 contain a bunch 

 of vesicular bo- 

 dies, attached by 

 short vascular pe- 

 dicles to a cir- 

 cumscribed por- 

 tion of its internal 

 surface (Jig. 216, 

 a). These vesi- 

 cles, the ovisacs 

 or calyces, as they 

 are called by com- 

 parative anato- 

 mists, are, in fact, 

 the nidi wherein 

 the ova are se- 

 creted ; and, if 

 examined shortly 

 before ovi position 

 commences, every 

 one of them is 

 seen to contain an ovum in a more or less advanced stage of deve- 

 lopement. In this condition the walls of the ovisacs are thick and 

 spongy; and their lining membrane, which constitutes the vas- 



d 



