GASTRODES PARASTTTCUM KOROTNl^I.-K. .S5 



body of Salpa should occur in a very younj]^ stage of the latter, when 

 the cellulose mantle is but slightly developed. The observation of the 

 planula stage noted above, as well as of the very young stages of the 

 parasite, however, shows that the infection may take place in the 

 advanced stage of the host. And, judging from the various sizes of the 

 examples of the parasite which may be found in one and the same 

 individual of the host, it is very likely that, the infection may occur at 

 various stages of the host. 



As to the change in the structure of the parasite after the entrance 

 into the body of the host, we may infer from the material at hand as 

 follows : — The planula which has bored into the body of the host will 

 make its way through the test and arrive at the mantle layer. Then it 

 will cast off the cilia, and the end of its cylindrical body directed inwards 

 will become concave and the body will grow gradually broader than 

 high, to assume finally a hemispherical shape. The parasite will undergo 

 development by taking nutriments from the host. The gastro-vascular 

 system, tentacular apparatus, aboral sense-organ and ribs ^^•ill develop 

 meanwhile, and the stage shown in PI. S, fig. i will be attained in time. 

 This represents, without doubt, the most advanced parasitic stage of the 

 animal. Very likely, the parasite will leave sooner or later the host 

 and become free. The eggs will be laid not very long after the 

 liberation. They will pass through the segmentation stage as usual. 

 But we have reason to assume that, the segmentation is somewhat 

 different from that which prevails in ordinary ctenophores and more or 

 less approximates the condition known in other coelenterates. The 

 structure of the ovarian ^g^, as well as the existence of the planula 

 stage, suggests this very much. At any rate, the e.gg will develop into 

 a planula which enters into the body of Salpa. These apparently 

 represent the ordinary developmental cycle of the animal. As to the 

 fate of the individual after the spawning, it is not impossible that, it 

 undergoes further development, and finally metamorphoses into an animal 

 looking quite different from the parasitic stage, although we have no 

 data at present to assure this. 



Systematic Position. 



Regarding the systematic position of Gastrodes, there can be no 

 doubt whatever, that it belongs to the Ctenophora, as Heider ('93) 

 has already pointed out. But to which order of the class should it be 



