942 PROTOZOA AND OTHER ANIMALS 



In connection with host-specificity among hypocomids, Jarocki's ob- 

 servation (1934, 1935) that Heterocineta jankkii is also a facultative 

 parasite on the oligochaete Chaetogaster Ihnnae'i is of considerable in- 

 terest. The oligochaete is usually present as an inquiline in the mantle 

 cavity of Physa fontinalis and other snails. The hypocomids are almost 

 always present on the snails; and they also infect almost all the oligo- 

 chaetes, attaching to various parts of the body and inserting the suctorial 

 tentacles into the hypodermal cells. Parasite-free worms quickly became 

 infected if brought into contact with ciliates either in or out of the 

 mantle cavity. Parasite-free Physa became infected if parasitized oli- 

 gochaetes were introduced into the mantle cavity. The worms pass 

 freely from one host to another, and thus facilitate the spread of the 

 infection. Chaetogaster Ihnnaei in other snails became facultatively para- 

 sitized by their specific hypocomids; but Heterocineta species could not 

 be introduced into unnatural hosts on the oligochaetes. To two other 

 species of Chaetogaster, Heterocineta janickii became attached tempo- 

 rarily, but soon dropped off. 



The Sphenophryidae (Fig. 200D-H) ) all occur on the gills of marine 

 lamellibranchs. They are sedentary, immobile, and nonciliated in the 

 adult phase. They are not true parasites; the relationship as defined by 

 Chatton and Lwoff (1921) is "inquilinism complicated by phoresy." 

 The ciliates are rather large, mostly flattened laterally, and adhere to the 

 surface by a long ventral edge (Fig. 200G). Sometimes they adhere 

 in a very precise and constant position, as Sphenophrya dosiniae in the 

 furrows separating adjacent branchial filaments of Dosinia exoleta (Fig. 

 200H). There is no mouth opening, and the ciliates apparently feed 

 osmotically; but Mjassnikowa (1930a) found evidence that S. sphaerii 

 ingests cells of the gill epithelium. She may, however, have misinter- 

 preted the nature of certain cytoplasmic spherules. Reproduction is by 

 development of motile buds. Cilia develop from the infraciliature, which 

 consists of a few rows of granules that are present in the vegetative indi- 

 vidual. 



An unusual sphenophryid is Gargarius gargarius, described by Chat- 

 ton and Lwoff (1934a) from Mytilus edulis at Roscoff. Rhynchophrya 

 cr/stallma from M. edulis in the Baltic Sea, of which a more complete 

 account was later given by Raabe (1935), is evidently the same ciliate 

 (Fig. 2001, J). Along one surface are two longitudinal, parallel, comb- 



