STINGING-CELLS IN OHASPEDOTE MEDUSA. 779 



einem vorspriiigenden Polster, das den Ocellarbildungen 

 andrer Meduseu entspricht, aber, Avie schon die alteren 

 Beobacliter (Alhnan, 16; Grobben 17) feststellten, keine 

 Ocellen entwickelt." 



In a young" medusa of Moerisia a slioi't time before its 

 liberation tlie manubrium is still without a moutli opening, 

 and. is clothed externally by a single layer of low ectodermal 

 cells (PI. 43, fig. 11), the internal lining consisting of large 

 clear endoderm cells containing nutritive spheres and occa- 

 sional irregularly shaped interstitial cells. The latter become 

 more numerous as development proceeds^ and some can be 

 clearly recognised by their enlarged nuclei to be sex-cells. 

 These at a later stage, no doubt, become transferred to tlie 

 ectoderm of the stomach region, and by their further division 

 form the gonad. Owing to the absence of individuals of the 

 right age, I am unable to state how the transference of sex- 

 cells from one layer to another takes place. I have never 

 met with them migrating through the structureless lamella, 

 and it is quite possible that the transference is a passive one,, 

 similar to that described by Goette in the male gonophores of 

 Hydr actinia (11, p. 70). In the youngest free- swimming 

 medusa examined by me the endoderm of the slightly 

 swollen stomach had lost its small cells, and was separated by 

 a very thin lamella from the ectoderm, which contained a few 

 rows of developing sex-cells. 



The endoderm slightly distal to this region had retained 

 a number of interstitial cells, some of which prove to be 

 obvious nematoblasts and contained developing nematocysts. 

 These are, of course, the rudiments of the fully formed 

 stinging-cells, which, as described in the first part of thi& 

 paper, are to be found in the endoderm, just below the 

 stomach of the adult medusa, and which later migrate to the 

 battery at the oral extremity of the manubrium. 



From this we must infer that the nematoblasts of the 

 manubi'ium arise in the endoderm of the developing gonophore 

 in exactly the same way as do the sex-cells ; like the latter 

 they are able to migrate through the tissues of the medusa. 



