118 Dr. M. Ussow on a new 



secondary buds [h) the increase by division of the free gene- 

 ration takes place very rapidly. The forms B and B^ appear 

 on the second or third day, and then, after a short delay, the 

 form «B appears on the fifth or sixth day. The last genera- 

 tion that I obtained («B" and aWh) appeared on the tenth or 

 twelfth day. This form remained constant during from eighteen 

 to twenty days ; but it is not impossible that under more favour- 

 able circumstances * it again repeats the mother- form, and 

 thus would furnish a third mother-generation (/3B) ; this, 

 however, is a mere supposition, proved by no facts. Be this 

 as it may, it seems to me that the facts collected by me indi- 

 cate that the future sexual animal is to be sought in the 

 grandchild-form bearing six tentacles, and that all the other 

 generations described may be called nutritive and nurse 

 forms f. 



Diagram to rejjresent the gradual increase of the different 

 generations of Polypodiura hydriforme. 



6=J} 



B' . . . B' 



B-=aB . . . B-i=aB 



aW = (/SB . . .) ? aWb={^B . . .) ? 



The power of replacing lost parts of the body is developed 

 in a very high degree in our animals j it is to be observed 

 most distinctly in the region of the tentacles. These, for 



* Notwithstanding tlie constant change of water by a stream in my 

 aquaria, we could not succeed in keeping all the described forms alive 

 longer than three weeks. Nourishment was apparently effected in the 

 normal way by spores and Infusoria; but nevertheless there was a want 

 of some conditions which I have not yet been able to make out. 



t If my supposition should prove correct, the whole cycle of develop- 

 ment of ruJt/podium hydriforme may be briefly expressed graphically in 

 the following way : — 



A— i— aB— C {i. e. B-, B^J, aB\ aW-b)—T)—K. 



From the hypothetical sexual form C originates the larva D, which 

 penetrates into the ovum of the Sterlet and then becomes converted into 

 the parasitic form A. 



