32 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



Faiire-Fremiet (1913) described the discharge of the nematocysts as a rup- 

 ture of the extreme anterior end of the capsule, with an eversion of the introvert 

 and a rapid unrolling of the filament. Chatton has given a much fuller de- 

 scription of this process and one that differs in some essential details from 

 our own. According to his interpretation, the filament is not an integral part 

 of the structure of the nematocyst, continuous at its base with the walls of the 

 introvert, but is a distinct structure. A the time of explosion the introvert is 

 forced outward, following a rupture of the extreme anterior end of the head 

 of the nematocyst, and the filament is throAATi out as a simple unrolling. He 

 figures no process at its posterior end by which its entire escape from the 

 nematocyst may be prevented. 



In these structures, which are similar in practically every detail to the 

 nematocysts of the Coelenterata (fig. H, 3), a similarity in their explosive action 

 is to be exiDected. That this similarity exists would seem to be borne out by 

 certain features in their structure and in the apj^earance of the exploded 

 organelle. In the hydroids additional structures, as short spines, are often 

 present within the coiled filament. In the exploded cell these are found on the 

 outer part of the filament, leaving no douljt as to the fact of its eversion as a 

 tube at the time of discharge (fig. H, 4). In the diuoflagellates no such struc- 

 tures exist, hence, as the actual process cannot be followed with the eye, the 

 manner of it must be inferred l)y analogy and by the appearances of the 

 nematocysts both before and after discharge. 



Our own interpretation of the explosion of the nematocysts is as follows: 

 Contact of the anterior end or head of the nematocyst with an appropriate 

 stimulus, such as sea water, causes its rupture with explosive abruptness, and 

 the introvert is thrown out. The rui^tured membrane remains like a collar 

 (fig. F, 3) around the basal portion of the introvert in its new position 

 (fig. F. 3, i>it.). As this latter structure is everted the stylet and thickened 

 basal portion (stij.) occupy the extreme anterior end of the nematocyst. 

 Simultaneously with this outward projection of the introvert the filament is 

 thrown out (fig. F, 3, fU.) as an everted long slender tube. In this position it 

 is found to be continuous with the anterior end of the nematocyst (fig. F, 3). 



The filament is a slender, doul)le-contoured thread, the tubular nature of 

 which is hard to demonstrate. That this is its structure would seem evident 

 from its appearance at the time of explosion of the nematocyst, and by analogy 

 with similar organs in the Cnidosporidia (Doflein, 1911) and in the hydroids 

 (Toppe, 1910) (fig. H). After explosion it is connected and apparently con- 

 tinuous with the walls of the nematocyst at the extreme anterior end of this 

 st]'i;cture. This is also shown in Chatton 's figures, one of which is reproduced 

 in our figure G, 10. 



As has ah-eady been pointed out, Chatton does not figiu'e any mechanism 

 by means of which the filament retains its relation with the nematocyst after 

 its explosion. A slender tlu'ead which has no organic connection with the 



