556 PTEEOPODA. 



(1488.) The manner in which the Clio uses these dental organs is 

 obvious from their anatomical position. The curved muscular cylinders 

 by the contraction of their walls force out the teeth, so that they then 

 project from the mouth, and are ready to seize and drag into the oral 

 orifice whatever food presents itself. 



(1489.) Once conveyed by the jaws into the interior of the mouth, 

 the prey seized is taken hold of by the tongue ; the free extremity and 

 upper surface of which is seen, when highly magnified, to be covered 

 with regular rows of spiny booklets, all directed backwards, and evi- 

 dently intended to assist in deglutition (fig. 278, B). 



(1490.) The structure of the alimentary canal is extremely simple. 

 The oesophagus (fig. 279, t) gradually dilates into a wide stomachal 

 cavity that is surrounded on all sides by the mass of the liver ; while 

 the intestine (v), in which the stomach terminates, mounting towards 

 the left side of the neck, ends by an external anal orifice. Two long 

 and slender salivary glands (w) are placed at the sides of the oesophagus, 

 and furnish a secretion that is poured into the mouth. The precise 

 character of the bile-ducts has not been satisfactorily determined in 

 Clio ; but in Pneumodermon, another Pteropod very nearly allied to the 

 genus we are describing, the stomach itself, which is enveloped on all 

 sides by the liver, receives the biliary secretion through a multitude of 

 minute pores. 



(1491.) With respect to the real nature of the respiratory apparatus 

 in Clio, much doubt exists. Cuvier regarded the aliform fins as being 

 subservient to respiration, as well as forming locomotive organs, and 

 observes that the surfaces of these appendages, seen with the micro- 

 scope, present a network of vessels so regular, so close, and so delicate, 

 that it is not possible to doubt that they are intended to perform the 

 functions of a respiratory apparatus, adding, moreover, that their con- 

 nexion with the internal vessels and the heart confirms this view of the 

 nature of these membranes. 



(1492.) Eschricht, on the contrary, denies altogether the existence of 

 any such vascular ramifications as Cuvier describes, asserting that the 

 appearance alluded to is entirely produced by the spreading out of the 

 muscular fibres above-mentioned, and that the only vessels visible in the 

 alar processes are a few arterial branches derived from the aorta. 



(1493.) We are still, therefore, in ignorance as to the respiratory 

 organs of Clio : the heart, however, is very apparent ; it is composed of 

 a single auricle and ventricle, enclosed in a pericardium (fig. 279, m), 

 and gives off at one extremity a large vessel (m), which Cuvier regarded 

 as a pulmonary vein, but which Eschricht has proved to be the aorta, 

 inasmuch as he has traced its branches to the liver and the other 

 internal viscera of the body. 



(1494.) The nervous system of this mollusk is easily distinguished, 

 not only on account of the large proportionate size of the ganglia, but 



