252 T. W. Engelmann on the Infusoria. 



ductive organs — an opinion Engelmann considers not improba- 

 ble, although he is unable to adduce any facts in confirmation 

 of it. 



Engelmann, moreover, has been able to follow out the re- 

 searches of Stein, Claparede, and Lachmann relative to the his- 

 tory of development in various hypotrichous and peritrichous 

 Infusoria. In Epistylis plicatilis he met with those buds from 

 the base, noticed by Stein, and called by Claparede Urnulae 

 (PI. III. fig. 10), remarkable for their acinetiform development. 

 They spring from the Epistylis at its junction with the pedicle, 

 exhibit a rigid and more dwarfed outline than do the ordinary 

 gemmae, which, on the contrary, elongate themselves, and take 

 on the ordinary characters of their parent. Engelmann witnessed 

 the transverse division of these Urnulae, but was unable to detect 

 their further development in this species of Epistylis. 



The same kind of organism is produced from the Epistylis 

 crassicollis. The rounded, sharply defined body of the Urnula is 

 enclosed in an oval, firm, and colourless sheath (PL III. fig. 10) 

 having a tapering posterior extremity, and terminated anteriorly 

 by a triangular aperture of moderate dimensions, through which 

 the animalcule protrudes a single moveable tentacle, or, rarely, 

 two such organs. In the interior of the animal a granular nu- 

 cleus and one or more contractile vesicles are discernible. A 

 transverse constriction followed by fission proceeds, and the an- 

 terior uniformly ciliated segment quits the sheath. The Urnula 

 has a very close resemblance to Acineta mystacina, differing from 

 it in no other respect than in the figure of its sheath and in 

 its primitive position. Claparede assumed it to be a member of 

 the family Rhizopoda, especially as he observed its tentacles 

 ramify. This circumstance is not deemed by Engelmann of 

 sufficient moment to induce its transfer to such a wholly different 

 class of animals from that with which in all other respects it 

 seems related. For, he asks, what Rhizopod has a sheath like 

 Urnula, or what Rhizopods can employ their pseudopodia as 

 sucking-tubules ? or which of them, again, can multiply them- 

 selves by means of ciliated fission-products, as the Urnula can 

 do ? But in all these peculiarities the Urnula coincides with the 

 true Acinetae ; whereas, if it were considered one of the Rhizo- 

 poda, it would be difficult to determine the boundary-line be- 

 tween this class and that of the Infusoria (Ciliata). The amphi- 

 leptoid cysts, first described by Claparede and afterwards by 

 Stein and Udekem in various Vorticellina, were seen by Engel- 

 mann also in Epistylis plicatilis. The Amphileptus underwent 

 fission within the cyst before leaving it. 



Similar Urnulae and amphileptoid cysts were encountered in 

 Epistylis crassicollis. In E. flavicans, which has a distinct oval 



