1086 PARASITES OF PROTOZOA 



Sphaerophyra and Endosphaera. In connection with them, it is interesting 

 to consider the important role they have played in the development of 

 protozoology. The Acineta theory and the embryo theory of ciliate devel- 

 opment held an important place in the thinking of protozoologists in 

 the third quarter of the nineteenth century. 



Stein's Acineta theory was in the first instance not related to parasitic 

 Suctoria. He came (1849, 1854) to the conclusion that free-living 

 acinetids are the result of metamorphosis of vorticellids, and that they 

 give rise to embryos from which the vorticella form is again produced. 

 This embryo production, of course, is the result of the internal budding 

 process characteristic of acinetids. This theory was successfully attacked 

 by Cienkowski (1855a), Lachmann (1856), and Claparede and Lach- 

 mann (1860-61). Stein later (1859) modified the Acineta theory as it 

 was originally stated, but still did not admit that acinetids are inde- 

 pendent organisms. The embryos of various Infusoria, he said, have all 

 the characteristics of acinetids; and he believed that various higher 

 Infusoria in their development pass through Acineta-like phases; for 

 example, that podophryids were developmental phases of Paramecium. 



Authors credit Focke (1844) with the first observation of the so-called 

 motile embryos. He discovered them in Varamecium bursaria, in which 

 they were soon found by many other observers. They were found also 

 in a variety of other Euciliata. As late as 1867, Stein could state that 

 "today no one can doubt that those Infusoria whose reproductive organ- 

 ization consists of nucleolus and nucleus are in fact hermaphrodites, the 

 nucleus playing the role of a female, the nucleolus of a male sex organ"; 

 and could maintain that the embryonal spheres were produced from the 

 nucleus. 



Stein's thesis, however, had already been discredited. Claparede and 

 Lachmann (1858-59) had described Sphaerophrya pusilla in water, 

 associated with numerous oxytrichids; yet they were not firm in their 

 opinion that Sphaerophrya might not be an embryo of Oxytricha. It was 

 the view of Balbiani (I860) that the so-called embryos of ciliates were 

 parasites belonging to the genus Sphaerophrya; and in support of this he 

 adduced his observations on entry into ciliates, and on the spread of an 

 infection among Paramecium by the introduction into a sound culture of 

 a few infected ciliates. Metschnikoff (1864) observed the cycle, from 

 separation from one Paramecium host through entry into another, and 



