Dr. L. Plate on the Genus Acinetoides. 20-5 



body from the species of Acinetoides, and, further, possessed 

 no sucking-tentacle. The conclusion that these were inde- 

 pendent organisms, and not mere developmental forms, was 

 therefore unavoidable, and it was afterwards confirmed by 

 the observation of the reproduction of Acinetoides zoothamni 

 by simple transverse fission. The individuals in course of 

 division sometimes swam about and sometimes remained 

 seated upon their food-animals ; but I did not succeed in the 

 latter case in observing a double sucking-tentacle. 



The reproduction by transverse division furnishes a further 

 proof of the intermediate position which the genus Acinetoides 

 occupies between the Ciliata and the Suctoria. Such a mode 

 of reproduction has indeed already been observed in various 

 other Acinetge, as in Podophrya fixa, Acineta mystacina, 

 Urnula epistylidis, and some others ; but it is nevertheless a 

 rare mode of increase among the Suctoria, quite subordinate 

 to the reproduction by external or internal budding ; while, on 

 the contrary, among the Ciliata the new individuals in general 

 originate by transverse or longitudinal division, and are pro- 

 duced as buds only in some attached genera. This contrast, 

 as regards reproduction, which exists between the Ciliated 

 Infusoria and the Acinetce is not principial, bat only caused 

 by the different mode of life. With respect to the possibility 

 of nourishment, a sessile organism is always at a disadvantage 

 as compared with one of the same structure but capable of 

 free locomotion, and therefore for the continuance of its species 

 requires a larger progeny, a purpose which is of course better 

 attained by the formation of numerous small buds than by 

 simple division, which furnishes only two descendants from 

 one parent-animal. 



What systematic position the genus Acinetoides ^ has to 

 occupy cannot be doubtful after what has been said ; it is to 

 be referred to the Suctoria and to be regarded as a transition- 

 form between these and the Ciliated Infusoria. The existence 

 of such an intermediate form, it ajypears to me, furnishes a 

 fresh argument in support of the opinion already maintained 

 by several naturalists, that the Acinetce are modified Ciliata, 

 which have acquired peculiar sucking and grasping filaments, 

 to be regarded as organs sui generis, in connexion with the 

 acquisition of a sessile or parasitic mode of life. This notion 

 is founded principally upon the fact that the buds of the 

 Acinetse resemble the true Infusoria in their holo-, hypo-, or 

 peritrichous coat of cilia, so that the Acinet* in their youth 

 pass through a ciliatiform stage. It has been urged against 

 this conception of the swarm-buds (I think erroneously) that 

 tiie so-called " biogenetic fundamental law " is not applicable 



