116 Dr. M. Ussow on a neio 



About the time of the breaking up of the stolo the muscular 

 fibres have acquired the appearance of broad, thin, very con- 

 tractile, smooth muscular bands, with thin edges touching 

 each other. 



Further in we come upon the unilamellar endoderm. 

 Nevertheless we observe between the endodermal cells, which 

 are rendered very turbid by the deposition of yolk-particles, 

 and the muscular layer, an interspace which is constantly 

 becoming more sharply marked. This fissure, which narrows 

 by the application of reagents and which extends to the 

 extreme tip of the tentacles, is filled with a clear fluid ; the 

 latter is traversed by a fine web of anastomosing protoplasmic 

 runners of the endodermal cells. During contractions of the 

 body and tentacles the lumen of this fissure becomes smaller, 

 which would indicate that these runners of the endodermal 

 cells are themselves also contractile. 



At the commencement of my investigation I was inclined to 

 regard the above structure as a kind of supporting lamella, 

 until I subsequently convinced myself that such a thing does 

 not exist in our animal. 



In the interior of the endodermal cells we find, besides their 

 large nucleus, many yolk- globules, and, further, a quantity of 

 dark- brown particles, which I would regard as a product of 

 the decomposition of the latter. 



It has already been remarked that during the breaking up 

 of the stolo all the bud-cavities are filled with yolk, and that 

 this passes through the ectoderm into the bud, for there are 

 no openings in the wall either of the buds or of the stolo ; and 

 a further proof of such an immigration of the yolk-globules is 

 furnished by the circumstance that in ova with developed 

 Polyj?odia furnished with everted tentacles no yolk is to be 

 met with outside the parasite. Consequently the noiirisJiment 

 of the buds individualized after the breaking-up of the stolo 

 is effected at the expense of the yoTk contained in their cavity ^ 

 and this cavity may then, especially after the breaking-through 

 of the buccal aperture, be designated the gastral cavity. Its 

 diverticula^ which are at first broad and then narrowed 

 conically, traverse the tentacles to their tips. 



Thus, to summarize what is stated above, we have in Poly- 

 podium hydriforme a vermiform body (A) on which are formed 

 first of all primary buds (a), and then from these secondary 

 ones (i), and which after five or six months of parasitic exist- 

 ence breaks up into thirty-two hydriforra organisms, living 

 free in the Volga, 2 millim. long and 4^ millim. broad, fur- 

 nished with twelve lateral and twelve inferior tentacles, 

 whence the name Polypodium hydriforme. The body-wall 



