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 



opy 



FIG. 193. Diagram of 

 the eye of a squid, Loligo, 

 a.o.c, anterior optic cham- 

 ber; c, cornea; ir, iris; 

 the eye is a fold which projects back- /, lens; /', external portion 



ward under the collar, and is probably J. lens; op ' gf optlc ^ n ~ 



< ghon ; p.o.c, posterior 

 olfactory. optic chamber; r, retina. 



Squids are either male or female. The , tk ^ isto c r a y mb ^ 

 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. 



