PHYLUM MOLLUSCA 



267 



which enters the mantle cavity flows over them, supplying oxy- 

 gen to the blood and carrying away carbon dioxide. 



The two nephridia or kidneys (Fig. 192, Ne) are white trian- 

 gular bodies extending forward from the region of the branchial 

 hearts and opening on either side of the intestine at the ends of 

 small papillae. 



The nervous system consists of a number of ganglia mostly in 

 the head. The principal ones are the supra-cesophageal, in- 

 fra-cesophageal, suprabuccal, infrabuccal, 

 stellate, and optic ganglia. 



The sensory organs are two very highly 

 developed eyes, two statocysts, and prob- 

 ably an olfactory organ. The statocysts 

 are two vesicles lying side by side in the 

 head ; each contains a concretion, the 

 statolith, and is probably an organ of 

 equilibrium. The eyes (Fig. 192, E ; 

 Fig. 193) are large and somewhat similar 

 superficially to those of vertebrates (com- 

 pare Fig. 193 with Fig. 351). Just behind 



the eye is a fold which projects back- J, lens; V, external portion 



ward under the collar, and is probably *£« J* .°^£ 



olfactory. optic chamber; r, retina. 



Squids are either male or female 

 reproductive organs (Fig. 192, Go) of the Grenacher.) 

 male are the testis', a vas deferens, a 



spermatophoric sac, which contains sperms bound together into 

 bundles called spermatophores, and a copulatory organ, the penis. 

 The female organs are an ovary, oviduct, oviducal gland, and 

 nidamental gland. 



b. Cephalopoda in General 



Classification. — The Cephalopoda may be divided into two 

 orders according to the number of gills, kidneys, and auricles, 

 and the character of the shell. 



_po.c 



Fig. 193. — Diagram of 

 the eye of a squid, Loligo, 

 a.o.c, anterior optic cham- 

 ber; c, cornea; ir, iris; 



rpi (From the Cambridge 

 Natural History, after 



