T. W. Engelmann on the Infusoria. 257 



and A. cucullulus. This consists in the breaking-up of the nu- 

 cleus into several spheroidal segments, from which a still larger 

 number of small ciliated germs derive their origin, distinguish- 

 able in no respect from the embryos of Epistylis plicatilis. 

 Claparede represents this offspring so derived as similar to the 

 usual form of Acineta-germs : but with this view Engelmann 

 cannot agree; for he maintains that both the mode of origin 

 and the nature of the mature germs so derived differ altogether 

 from those of the xisual offspring of Acineta. Thus it is a cir- 

 cumstance of much weight that these little Acineta-embryos 

 derive their substance entirely from the nucleus, and receive no 

 addition from the parenchyma of the parent animalcule. Again, 

 they exhibit this peculiarity in their formation in common 

 with the embryos of ciliated Infusoria, as, for instance, with 

 those of Vorticellina ; and if their external resemblance to these 

 latter be also considered, we must admit the existence of a 

 remarkable similarity between the embryonic development of 

 Ciliata and that form of the reproduction of Acineta by these 

 remarkable little germs. This being granted, it has an import- 

 ant bearing upon Stein's celebrated hypothesis of Acinetiform 

 development of Infusoria. To show, for example, that the little 

 Acineta-products in question are true embryos developed by a 

 sexual reproductive act, is to overturn the Acineta-theory. On 

 the other hand, if, as is possible, and as the completely similar 

 organization of the little offspring of Acineta quadripartita to the 

 embryos of Epistylis plicatilis intimates, this method of develop- 

 ment has a special character, and is concerned in a transforma- 

 tion of the Acineta back again into ciliated Infusoria, then the 

 Acineta-theory becomes established. Future researches must 

 decide this difficult problem. 



As an appendix to his general remarks on the organization 

 and reproduction of Infusoria, Engelmann appends a systematic 

 history of several new genera and species he has discovered. 

 The new genera named and described are Chasmatostoma, Micro- 

 thorax, Drepanostoma, Gastrostyla, and Astylozoon ; and the new 

 species of previously described genera are Lacrymaria elegans, 

 Conchophihirus (PL III. fig. 15) curtus, Pleurotricha setifera, Uro- 

 leptusmobilis, U.agilis, Oxytricha strenua, 0. parallela, Carchesium 

 Aselli, and Epistylis nympharum. 



The new genera are thus severally characterized : — 



Chasmatostoma. PL III. fig. 16. 



Figure constant, reniform, somewhat compressed, uniformly 

 ciliated. A small oval oral aperture, having an undulating 

 membrane affixed within it, occupies the middle of the flat 

 ventral surface. 



Ann. # Mag. N. Hist. Ser. 3. Vol. x. 18 



