244 PTEROPODA. PART in. 



then on the other. In calm weather, they come to the 

 surface in myriads, and quickly descend again. There 

 is a pair of slender tentacles close to the head, which 

 are organs of feeling, a pair of eyes are placed on the 

 back of the neck, and acoustic vesicles lined with cilia 

 keep otolites in motion. Besides these organs of sense, 

 the Clione has respiratory, digestive, and nervous sys- 

 tems. The latter consists of a nerve-collar round the 

 gullet, with two nerve masses in its upper part, so the 

 Clione is well supplied with nerves. 



Upon each of the two round lobes of the head, there 

 are three tentacles, totally different from those of feel- 

 ing. They are, in fact, organs of prehension, which can 

 be protruded or withdrawn at pleasure into a fold of the 

 skin. When protruded, these six tentacles form a 

 radiating crown round the mouth, which is terminal, 

 and furnished with fleshy lips. Each of these tentacles is 

 perforated by numerous cavities, appearing like red spots 

 to the naked eye; however, Professor Eschricht dis- 

 covered that each spot consists of a transparent sheath, 

 enclosing a central body composed of a stem terminated 

 by a tuft of about twenty microscopic suckers, capable 

 of being thrust out to seize prey. The whole number 

 of these prehensile suckers in the head of one Clione was 

 estimated by Eschricht to amount to 330,000. Not- 

 withstanding the vast prehensile power and multitude 

 of these animals, they find abundance of food in the 

 Arctic Ocean, for although the water is generally of the 

 purest ultramarine blue, one fourth of the Greenland 

 Sea, extending over 10 of latitude and some hundred 

 feet deep, is green and turbid, with a profusion of 

 minute animal life. The indefinite increase of the 

 Clione borealis is checked by the whales, who feed 

 upon them, and other minute inhabitants of the Arctic 

 Seas. The Pteropods first appear in a fossil state in 

 the Lower Silurian strata. 



