1903.1 



On the Nematocysts of Solids. 



481 



small nematocysts of the tentacles usually remain undischarged; even the 

 large nematocysts found at the base of the tentacles of many hydroids 

 (Eudendrium) are often not discharged unless the polyps are teased 

 up, compressed or otherwise stimulated. It is quite possible, therefore, 

 that no attempt is made by the prey to discharge its nematocysts till 

 it has been swallowed by the ^Eolid and immersed in juices of sufficient 

 concentration to prevent the discharge. Perhaps a preliminary covering 

 of mucus may help to delay the discharge. 



Cn.bi. 



Emb. 



On the other hand, since it is known that the thread of a developing 

 nematocyst is formed outside the capsule and is only inverted when 

 complete, presumably by the extraction of water from the capsule 

 by the surrounding protoplasm, it is quite possible that the gastric 

 juices of an ^Eolid may have the same effect on a discharged nema- 

 tocyst. 



Development and Structure of the Cnidocysts. 



Thanks to Davenport, Hecht and Krembzow, the origin of the 

 cnidosacs from the distal extremities of the ceratal diverticula of the 

 gastric gland is thoroughly established, and the general outline of its 

 development known. What observations, however, have been made on 



