100 THE ANATOMY OF LWERTEBRATED ANIMALS. 



their detachment from the maternal organism ; and I have 

 been able to assure myself that, after having lost their ten- 

 tacles, becoming clothed with vibratile cilia, and acquiring a 

 mouth, which makes its appearance as a longitudinal groove, 

 thej return definitely to the parental form, developing in 

 their interior the green granules which are characteristic of 

 this Paramoecium^ without undergoing any more extensive 

 metamorphosis." 



In Figs. 19-22 of Plate IV., which accompanies his paper,* 

 Balbiani figures all the stages by which the acinetiform em- 

 hTyo becomes a Paramoecium. 



So far as the fact of conjugation, the changes in the " nu- 

 cleolus," and the development of filaments in it, with the 

 subsequent detachment, by division, of masses from the " nu- 

 cleus," are concerned, these statements have not been modi- 

 fied by M. Balbiani, while they are fully confirmed by the ob- 

 servations made by himself, Claparede and Lachmann, Stein, 

 KoUiker, and others, in Paramoecium hursaria, P. aurelia^ 

 and other ciliated Infusoria. 



In the closely allied Paramoecium aurella, the occurrence 

 of the various stages of conjugation, conversion of the " nu- 

 cleolus " into bundles of spermatozoa, and subsequent division 

 of the " nucleus," is also established by the coincident testi- 

 mony of Balbiani and Stein. Balbiani affirms that, in this spe- 

 cies, the clear globular bodies which result from the division 

 of the " nucleus " pass out of the body vrithout undergoing 

 any further modification, and he considers them to be ovules. 

 Stein also admits that he has never seen acinetiform embryos 

 in this species. 



But, as it would seem, on the strength of these negative 

 observations in Paramoecium aurelia, Balbiani, in his later 

 publications, asserts that the " acinetiform embryos " observed 

 not only in Paramoecium^ but in Stylonychia^ Stentor, and 

 many other ciliated Infusoria^ are not embryos at all, but 

 parasitic Acinetoe ; and he makes this assertion without ex- 

 plicitly withdrawing the statement given above of his own ob- 

 servation of the passage of the acinetiform embryo of Para- 

 moecium hursaria into the parental form. Engelmann and 

 Stein, on the other hand, hold by Balbiani's original doctrine, 

 and give strong reasons for so doing. Among the most for- 

 cible analogical arguments are those afforded by the process of 

 sexual reproduction observed by Stein in the peritrichous In- 

 fusoria. 



In the Peritricha ( Yorticellidce^ Ophrydidoe^ Trichodidce) 



