Form of Freshwater Goelenterate. 121 



freely into the internal space, and perhaps constitutes a primi- 

 tive infundibuliform stumach-tube. In the formation of the 

 buccal opening the endoderm passes directly into the ectoderm. 

 On passing into the tentacles and in their further course in 

 these the endodermal cells coalesce here and there, in conse- 

 quence of which the lumen becomes very indistinct. A 

 similar intimate union of the endodermal elements occurs also 

 in the large interior spaces (two paired lateral gastral pouches) 

 of the generations B and B^. 



3. I'he mesoderm, which runs between the ectoderm and 

 entoderm in the form of a muscle-fibre layer scarcely percep- 

 tible in transverse sections, is strongest in the proboscis and 

 at the points of attachment of the teiitacles. At the transverse 

 furrows of the aboral end of the body, on the other hand, the 

 muscle -libre layer appears to be rudimentary. These condi- 

 tions are brought about by the altered mode of life of our 

 animal, which now, as already remarked, rests upon the 

 tentacles and moves about with their assistance. 



As regards the contractile processes of the endodermal cells, 

 which traverse the fissure between the endoderm and meso- 

 derm perpendicularly to the body- layer, the free-living Poly- 

 podium presents about the same picture as the buds of the 

 parasite. 



Appendix. 



On my return to Kasan I obtained five Sterlets, all with 

 roes, on the 5th September^ and in three of them I found the 

 following : — 



1. An unusually developed state of the secondary buds {h) 

 for this season of the year. Many of these were in the phase 

 in which the tentacles are everted. Two ova contained stolons 

 with perfectly developed buds. After being transferred into 

 flowing water one of the stolons perished on the same day, 

 while the others divided quite normally into individuals of 

 the generation B, which lived for a whole week in the aqua- 

 rium. What may have been the cause of these specimens 

 having remained retrograde in their development at the 

 spawning-time of the Sterlet in the preceding May is a ques- 

 tion difficult to decide, and it is at any rate to be supposed 

 that these buds must have perished, as it would have been 

 only in next May that they would have had the opportunity 

 of quitting the ovum and acquiring their freedom, during the 

 spawning of the Sterlet. 



2. Among the infected ova I found, on the 6th of Septem- 

 ber, two smaller examples, each of which contained a larva 



