INTR OD UC TION I 3 



served that decaying flesh apparently breaks into minute granules 

 (bacteria). Influenced no ^oubt by the teachings of the nature-phi- 

 losophers, Buffon and Oken, he further thought that he had observed 

 the formation of larger forms of life from these minute granules, and 

 among them, some Podophryas, which changed into Vorticellas, and 

 these again into Oxytrichinas. 



Stein's famous Acineta-theory was first brought out in his work of 

 1849, m which he described the many division phases of Vorticella, 

 and gave a very good account of the process of encystment. The 

 encysted animal, he thought, breaks down into a great number of 

 minute particles, having at first the form of certain flagellates, which 

 develop into young Vorticellas. Later he adopted a second hypothe- 

 sis, equally untenable, viz. that Acineta is derived from the cysts of 

 Vorticella. This conclusion was based upon the fact that he had seen 

 the preparatory stages of encystment of the Suctorian Podophrya, 

 which he thought were transition phases from the encysted condition 

 to the adult free Podophrya, while the cysts from which he supposed 

 they had come he thought were formed by Vorticellas. Generalizing 

 from this supposed fact, and seeing supposed confirmation in many 

 different directions, he finally regarded the entire division of the Suc- 

 toria as merely reproductive phases of the genus Vorticella. An 

 apparent support for his theory was found in 1854, when he discov- 

 ered the ciliated embryos in Suctoria, which closely resemble the 

 Vorticellidae. Not once did he follow out the development of these 

 embryos by actual observation ; it was purely hypothetical, and the 

 discovery of Acineta embryos, since found to be parasites in various 

 other ciliates, only strengthened him in this point of view. 



Stein's theory soon found opponents. Perty ('52) feebly opposed 

 it, while Johannes Miiller and his pupils, Claparede and Lachmann, 

 and Cienkowsky ('55) traced the development of the supposed young 

 Vorticellas to the adult forms of Suctoria. The theory was finally 

 completely overturned by Lachmann ('56) and Balbiani ('60), the 

 former showing by actual observation that neither does Vorticella 

 develop into Acineta, nor do embryos of the latter develop into Vor- 

 ticella, while the latter discovered that the supposed embryos are in 

 reality parasitic Suctoria, a view in which he was ably supported by 

 Metchnikoff ('54) and Kolliker ('64). 



Balbiani's researches in the life history of the Protozoa at first led 

 him into a curious error, a reminiscence apparently of Ehrenberg's 

 and the older point of view. O. F. Miiller had observed and cor- 

 rectly interpreted conjugation in different forms, but his successors 

 down to Balbiani regarded this interpretation as incorrect, maintain- 

 ing that he had seen only stages in simple division. Balbiani ('61) 

 returned to M tiller's view, and clearly stated that, in addition to 



