1903.] 



On the Nematocysts of ^Eolids. 



483 



of the cnidosac. When the cyst is completed both the cnidoblast and 

 the associated intermediate cells undergo degeneration, so that in the 

 older parts of the cnidosac each cnidocyst consists simply of a 

 membranous bag, containing nematocysts, which are often apparently 

 attached to its inner wall to keep them in place, and -a more or less 

 degenerate cnidoblast while wedged between adjacent cnidocysts are 

 found small darkly staining bodies, the remains of the intermediate 

 cells (fig. 13). 



Summary. 



The facts brought forward as evidencejthat the nematocystsjof Solids 

 are derived from their prey are as follows : 



1. Not only are nematocysts of Solids and Ccelenterates identical in 

 plan of construction and mode of discharge, but each of several 

 distinct types occurs in both groups. 



2 A single type of nematocyst does not occur uniformly throughout 



a species, but different individuals of the>me species may have 

 quite different nematocysts ; moreover, a single individual may 

 have nematocysts of several different types, found in as many 

 distinct species or groups of Ccelenterates. 



3 When it is known on what Ccelenterate an .Solid has recently 



been feeding, the nematocysts of the two are found to 1 



