Vlll PREFACE. 



processes that distinguish this family. On the other hand M. J. 

 D'UDEKEM (M6m. sur le developpement des Infus. in Mem. de V Acad. 

 de Bruxelles 1857) has shewn that Epistylis plicatilis in the course 

 of its multiplication by metamorphosis, does pass through the 

 form of Acineta, and in it develops an internal ciliated germ. At 

 all events, it is established by different observers that, in addition 

 to multiplication by fission and gemmation, infusories also pro- 

 pagate embryos in the formation of which the nucleus is con- 

 cerned. 



Prof. LEUCKART would reject the first and third of VAN DER 

 HOEVEN'S orders of Infusories, excepting only the PeripJirygana 

 which, by a modification of the definition of the fourth order he 

 would receive into it, the rest being referred to lower forms of Algce, 

 &c. But this proceeding would seem to be premature, for a number 

 of the Atricha have been seen to take in food, as by COHN, Nov. 

 Act. Acad. Leop. Car. xxu. P. i. p. 182, and LACHMANN 1. 1. p. 

 167, in Monads and Cryptomonads, arid J. MUELLER and others in 

 Bodo grandis or an Astasia. In the former the mouth was observed 

 close to the insertion of a flagelliform appendage and the vent at the 

 posterior extremity. According to LACHMANN at least one con- 

 tractile vesicle may be seen in all the transparent individuals of 

 this family, whilst a similar vesicle has been observed by BUSK 

 in Volvox (Quarterly Journ. of Microscop. Soc. I. 1853) and by 

 CLAPAREDE in several species of Euglena. LACHMANN contends 

 that no such pulsating spaces have been found hitherto in any 

 vegetable cell or in the spore of any undoubted plant (1. 1. p. 369), 

 and he agrees with SCHNEIDER that creatures thus constituted 

 ought to be placed amongst animal Infusories until it be distinctly 

 shewn that such organs exist also in undoubted vegetable cells. 

 See A. SCHNEIDER Beitrdge zur Naturgesch. der Infusorien in MUEL- 

 LER'S Archiv 1854, pp. 191207. 



The argument for the animal nature of all organisms present- 

 ing pulsatory spaces is strengthened by the fact that in very many 

 instances vessels have been shewn to be in connexion with these 

 spaces or vesicles, and hence by the probable inference that where 

 there is a pulsatory vesicle there also a vascular system exists. 



The opinion of 0. SCHMIDT, Vergl. Anat. p. 250, that the pul- 

 satory vesicle opens externally, has not been confirmed by other 

 observers; and appears to be directly contradicted by what is seen 



