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TEXTBOOK OF ZOOLOGY 



system, which is closed, is composed of arteries, veins, and two 

 branchial hearts. Blood is oxygenated in two feathery gills which 

 project into the mantle cavity. The two light-colored triangular 

 kidneys are situated anterior to the branchial hearts and discharge 

 their contents through small papillae, one located on each side of 

 the intestine. In squids the sexes are separate. The male repro- 

 ductive system is composed of a testis, vas deferens, spermatophoric 

 sac, and penis ; the female system consists of an ovary, oviduct, 

 ovidueal gland, and nidamental gland. 



-- Cornea 

 Eyelid 



Iris 



Lens 



— Ciliary M. 



^ Retina 



Optic (ganglion 



Fig. 150.- 



-Longitudinal section through eye of squid. (Redrawn and modified after 

 Borradaile and Potts by permission of The Macmillan Co.) 



The nervous system of cephalopods shows a high degree of spe- 

 cialization when compared with the nervous system of other mol- 

 lusks. The "brain" is composed of a close association of ganglia 

 around the esophagus and is protected by a capsule of tough tissue 

 resembling cartilage. Nerves radiate out from the central nerve 

 mass to the various parts of the body ; some of the nerves terminate 

 in large ganglia, such as the stellate ganglia in the mantle. The 

 eyes of the squid are supported by pieces of "cartilage" and are 

 relatively complicated. Statocysts, which are similar but more 

 complicated than those described for the clam, are situated near 

 the brain mass. Ciliated pits which are supposed to be olfactory 

 in function open in the form of a slit just back of each eye. 



