PARASITES OF PROTOZOA 1087 



considered the parasite nature of the so-called embryos to be completely 

 proved. 



Sphaerophrya shows suctorian characteristics in the presence of tenta- 

 cles. The so-called embryos of certain vorticellids, however, do not have 

 this characteristic; they are simple spherical or ovoidal bodies with 

 equatorial bands of cilia. Stein (1867), in his efforts to combat Balbiani, 

 had only weak arguments against the parasitic nature of the Sphaero- 

 phyra-type "embryos"; but he was firm in his conviction that the "em- 

 bryos" of vorticellids {Epistylis plicatilis) could not be parasitic Infu- 

 soria. Such a concept, he stated, would be ludicrous. Engelmann (1876), 

 reviewing the whole question in support of the parasite theory (which 

 he had vigorously opposed in 1862), reported having observed the 

 entry of the supposed non-tentaculated embryos of Vorticella microstoma 

 into that host. Thus he proved the parasitic nature of that organism also, 

 a view also stated by Biitschli ( 1876) , and gave it the name Endosphaera. 



The endozoic forms of Sphaerophrya are but little modified in conse- 

 quence of parasitism, and the majority of species of the genus are 

 entirely free-living. S. stentorh Maupas is free-living or parasitic in 

 species of Stentor; recently Kalmus (1928) reported it in S. roeseli. The 

 parasites of other ciliates have all been placed in a second species, which 

 also is either free-living or endozoic. Biitschli (1889) and Sand (1899) 

 identified this second species with Claparede and Lachmann's free-living 

 S. pus ilia. Collin ( 1912) , however, considered it to be S. sol Metchnikoff 

 which also was originally described as a strictly free-living species. 

 Sand regarded S. sol as a synonym of 5". ptisilla. 



Species of the genus Sphaerophrya differ from those of Podophrya 

 in the absence of a stalk. The body is spheroidal or ellipsoidal, and 

 tentacles radiate from the entire surface. Reproduction is by equal or 

 unequal fission or by external budding, except in S. stentoris, which is 

 reported to show a transition to internal budding. The free-swimming 

 forms produced by budding are provided with cilia that are localized 

 at one extremity, in a girdle, or generally distributed; and they possess 

 tentacles. This form, in parasitic phases, penetrates the surface of a 

 ciliate and takes up a position in the cytoplasm, losing cilia and tentacles. 

 There reproduction by division and budding takes place. 



Endosphaera (Fig. 225) has become more closely adapted to para- 

 sitism. It does not occur as a free-living organism, except briefly in the 



