322 



MOLLUSCA 



[CH. 



fertilizing the female the male inserts this arm into his own mantle- 

 cavity and receives on to it the spermatophores from his own genital 

 duct. He then inserts it in the mantle-cavity of the female and 

 deposits the spermatophores in a depression of her skin -either on 

 the head or near the opening of the oviduct. In other genera such 

 as Argonauts the modification of this arm is much more pronounced 

 the basal portion loses its suckers and is converted into a sac. 

 During copulation this arm is amputated and left in the mantle- 

 cavity of the female. It was found there by Cuvier who mistook 

 it for a Trematode worm and called it Hectocotylus (literally 

 hundred suckers). Hence this arm in all genera even in Sepia 

 where the modification is slight is termed the hectocotylized arm. 



FIG. 149. Side view of Nautilus pompilius x . After Graham Kerr. Half the 

 shell has been removed to expose the animal and the chambers of the shell. 



1. Last completed chamber of the shell. 2. Hood part of foot. 3. Shell 

 muscle. 4. Mantle cut away to expose (5) the pin-hole eye. 6. Outer 

 wall of shell, some of which is cut away to show the chambers. 7. Siphon. 

 8. Tentaculiferous lobes of the foot. 9. Funnel. 



The oviduct is simple, but in the female there are four glands, 

 the nidamental glands, situated on the wall of the mantle cavity 

 just outside the kidneys (18, Fig. 148). From the secretion of these 

 glands tough egg-shells resembling india-rubber cases are made. 

 The egg is about the size of a pea and when the young cuttle-fish 

 emerges it is already like the adult. 



Cuttle-fish feed chiefly on crabs, shrimps and other Arthropoda, 

 using their beaks to break the hard shell. Some are large enough 

 to attack men and this circumstance has given rise to many legends. 

 Gigantic species are sometimes cast dead on the shores of Nova 

 Scotia, the length of body being ten feet, and of the arms over fifty 

 feet. The phylum Mollusca finds its climax in the cuttle-fishes. 



