ßl2 William Patten 



which bave not lost, meantime, any of their characteristic color or 

 appearauce. 



The nuclei of the hypodermis iuvariably coutain nucleoli, with the 

 exception possibly of those which are so constricted that it is impossible 

 to determine whether nucleoli are present or not. The nuclei of the 

 pigmented band are situated close to the inner ends of the cells and 

 are distinguished by absorbiug staining fluids more deeply and evenly 

 than those of the unpigmented portions. 



It has been known since Will's time, that the ends of the tentacles 

 can be in-, or e-vaginated at pleasure. The former process is accom- 

 plishedbythe contraction oflongitudinal muscularfibres.the thickened, 

 nucleated ends of which form a muscular ring attached to the inner 

 surface of the hypodermis at the apex of the tentacle. By the con- 

 tractiou of these muscles only that part of the apex away from the eye 

 will be invaginated. Even in the most extended natural condition, the 

 tip of the tentacles is never convex, but on the contrary, slightly con- 

 cave, as represented in fig. 112. 



Still further contraction draws the pigmented band over the open- 

 ing of the eye in such a manner as to prevent the access of light to it. 

 Will was the one, who, in this case as in so many others, gave us the 

 first description of these structures, and correctly considered them as 

 visual Organs. His description of their external characters is perfectly 

 correct, as far as it goes ; to this account nothing has been added up to 

 the present day. 



Carrière has also examined these structures and asserts that 

 they are not eyes. Although he is careful not to call them luminous 

 Organs, one can see that he is inclined to lay stress upon the lumino- 

 sity of some of the cells. He says, for instance, p. 97. «Augen jedoch 

 sind es nicht unddesshalb kann ich an dieser Stelle keine eingehendere 

 Beschreibung der leuchtenden Zellen des Epithels und der Tentakel- 

 spitze geben. Ich glaubte nun Leuchtorgane vor mir zu haben. 

 Schließt man aber das Licht gänzlich ab, so erlischt der 

 Glanz und es findet hier somit keine selbständige Lichtentwicklung 

 statt. 'f 



Sharp has been less successful than Carrière in finding the 

 eyes of Cardium ; he declares that none are present in either C. edule, 

 C. muricatum, or C. magnimi; this, however. is probably due to the fact 

 that he only examined specimens preserved in alcohol, which quickly 

 dissolves the red pigment; one may then easily fall to see the lens 



