CHAPTER I: THE MANY-ARMED MOLLUSKS 



Class Cephalopoda 



Highly organised marine mollusks, of carnivorous habits, 

 moderate to large size, and of great strength and swiftness of 

 motion. Shell absent, except in Nautilus. Body cylindrical or 

 bag-like, bilaterally symmetrical. Head encircled by arms or 

 tentacles which are furnished with sucking disks or hooks. 

 Mouth fitted with horny beak, and toothed radula. Ink-bag 

 present, except in Nautilus. Funnel expels water from mantle 

 cavity and propels body backward through the water. Res- 

 piration by gills. Skin contains pigment spots by which colour 

 of body is changed at will. Reproduction system complex. 

 Sexes separate. Hectocotylised arm in male contains spermato- 

 phores. Organs of smell and of hearing present. Eyes complex. 

 Foot modified into tentacles and siphon. Nervous system cen- 

 tralised; main ganglia protected by cartilaginous case. 



This "head-footed" group of marine animals are so different 

 in their external character from the univalves and bivalves as to 

 raise this serious question : " Is it not all wrong to class them 

 with the mollusks?" With the exception of the Nautilus no mod- 

 ern cephalopod has an external shell such as snails and clams have. 

 Instead, there is in a large proportion of the group an internal 

 shell, familiar to us in the chalky "cuttle bone" of Sepia and the 

 transparent "pen" of the squid. The complicated eye, the 

 highly organized nervous and reproductive systems, also suggest 

 relationship with vertebrates. 



The predatory life led by these mollusks, their remarkable 

 strength, agility and skill in running down their prey and in escap- 

 ing enemies, the wonderful mechanism of the funnel, the button- 

 and-button-hole system that opens and closes the mantle chamber 

 in certain genera, the sucking disks, retractile hooks, and cushions 

 on the arms of others, all give proof of high specialisation. 



But the alimentary system, the beak and rasping, toothed 

 tongue, the siphon, and mantle and gills are all molluscan char- 



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