Minute Anatomy of the Infusoria. 475 



however, on account of the minute size of the embryo, I endea- 

 voured in vain to make these out with certainty. 



Often it seemed as if the anterior end were covered with very 

 short cilia ; possibly, however, the repulsion of any fine granules 

 which ap})roached this part might arise from such a Glabellar 

 organ as that possessed by the monads. 



After these observations, the change of Vorticella-cysts into 

 Acineta-forms might again appear doubtful ; but I was not to be 

 led astray by these considerations, especially since the one me- 

 thod of propagation did not necessarily exclude the other. On 

 the other hand, I followed out day by day the innumerable Vor- 

 ticella-cysts still contained in my iniusion, and, within ten days, 

 1 had the satisfaction of finding the first Acineta-forms, whose 

 number now daily greatly increased. joa 



The above-described formation of young within the Acineiee 

 was also frequently observed in the course of a few days more. 



There can now be no difficulty, after this long series of obser- 

 vations so frequently repeated and confirmed, in summing up 

 and justly expounding the whole cycle of the development of the 

 Vorticellce. From my observations it is incontestable that the 

 nucleus — the testis according to Ehrenberg — is the true and 

 only organ of propagation of the Infusoria, and may thence be 

 called henceforward the germ-nucleus (Keim-kern, nucleus ger- 

 minativus). A gland it is not, but a sharply defined homo- 

 geneous mass of fine granules like the nucleus in the interior of 

 a cell, and like this, probably bounded by a membrane in its most 

 perfect condition. That, further, the fine granules in the inte- 

 rior of the body of an Infusorium never perform the part of ova, 

 is just as certain, for in the last-described mode of development 

 of the Vorticella-cysts we have seen them one and all dissolved. 



With the '' testis " the " vesiculse seminales^^ of Ehrenberg 

 must equally be given up, — those clear spaces in the interior of 

 the Infusoria, which in a note above I have stated to be nothing 

 but spaces filled with a clear fluid. 



From the " germ-nucleus ^' new animals proceed in two modes 

 and of two forms. In each case the parental Vorticella must be- 

 come invested by a capsule, and its body change into a simple 

 globular vesicle. In each case the globular vesicle subsequently 

 enlarges, in order, either with a change in the wall of the cap- 

 sule to become a stalked or unstalked Acineta-form, or in order 

 to burst the wall of the capsule and to set free the embryos 

 arising from the breaking up of the germ-nucleus. 



These embryos have at most the size of the very youngest 

 For/zce//« observed by Ehrenberg* and myself f, which also pre- 



* Die Infusions-thiere, tab. 25. 3. 1 a. t hoc. cif. p. 98. 



31* 



