472 Prof. Stein on the Development and 



VorticellcB thus changed, ultimately became Acineta-like bodies, 

 by the included vesicular Vorticella-body extending itself some- 

 times on one side, sometimes on all sides, and thrusting out pro- 

 cesses of its wall, thus thinned. In this manner by one-sided 

 extension, the form described by Ehrenberg under the name of 

 Podophrya fixa as an independent species is produced, and by 

 the universal extension, one resembling the Actinophrys Sol of 

 Ehrenberg. I have since repeated this observation too often to 

 fear that it can be erroneous. Soon after that discovery, however, 

 I recognised the purpose of this change of the Vorticella-cysts 

 into Acineta, The nucleus of the Acinetce, or what is the same 

 thing, the original Vorticella, becomes entirely metamorphosed 

 into an actively rotating offspring ; becoming contracted into an 

 ovate body, which at its more pointed end carries a circlet of 

 long vibrating cilia, and at its more obtuse end is perforated by 

 a mouth which communicates with a distinct oral cavity. In the 

 interior of this offspring we observe already a long, oval, slightly 

 bent nucleus, and a round rhythmically contracting space*. It 

 perfectly resembles, in fact, a young Vorticella which has be- 

 come developed from a bud and is just ready to leave its parent. 

 Even if the change of Vorticella-cysts into Acinetce could be 

 questioned, yet every doubt must disappear when we compare 

 the offspring of the Acineta with the offspring of a Vorticella by 

 gemmation, or even with a fully-developed contracted Vorticella, 

 which is in the act of becoming freed from its stalk. As both 

 the former and the latter commonly soon become fixed, and pro- 

 duce a stalk from their posterior extremities, so without doubt 

 does the offspring of the Acineta become fixed when it has left 

 the Acineta. Since the time at which these observations were 

 first made, I have observed many hundred Acinetce with rotating 

 young, and have sometimes seen the offspring voluntarily ejected, 

 sometimes have pressed it out of the Acineta. The gap, which 

 the young tears in its passage through the wall of the Acineta, 

 becomes immediately closed again. The latter goes on stretch- 

 ing out and retracting its radiating filaments, like feelers, and 

 after a time produces in its interior a new nucleus for a second 

 offspring. 



Besides this propagation of Vorticella by means of Acineta 



* The presence of a contractile space in Infusoria, completely excluded 

 from the outer world, might of itself be considered sufficient to contradict 

 the view of O. Schmidt (Handbuch d. Vergleichende Anatomic, p. 220), 

 that the contractile spaces are vesicles opening externally at the surface of 

 the body and intended to pump in water. I say " contractile spaces or cavi- 

 ties " instead of " vesicles " advisedly, because I could never see any in- 

 vesting membrane around the clear space, and because I know Infusorial 

 structures with many contractile spaces which occupy no determinate loca- 

 lity, but move backwards and forwards. 



