946 PROTOZOA AND OTHER ANIMALS 



forms according to the negative characteristic of absence of a cytostome, 

 as ciliates of quite divergent relationships may have suffered regression 

 of that structure. Since a cytostome is not absent in free-Hving ciliates, 

 even of the most primitive type, it seems most likely that there has been 

 regression, rather than that lack of it is a primitive condition. Further- 

 more, we have to take account of the fact that oral structures may oc- 

 casionally have been overlooked. 



Cepede (1910) removed the opalinids from the group, and since then 

 several other genera have been excluded. The Ptychostomidae have 

 gone; in them the mouth structures are not absent, as at first supposed. 

 Protophrya appears to have affinities with the Thigmotricha. Chatton and 

 Lwoff (1935) stated that Metaphrya sagittae from the coelomic cavity 

 of Sagittct sp. is an apostome; and Kofoidella eleutheriae may also be a 

 foettingeriid. The description of Kofoidella, from the gastrovascular 

 canals of a medusa, is too inadequate for systematic purposes; but so far 

 as it goes relationship to Pericaryon, from the gastrovascular canals of 

 Cestus veneris, is not excluded. The macronucleus is described as com- 

 pact and central, and quite variable in size. The macronucleus of Peri- 

 caryon cesticola is reticular and peripheral; but it is not impossible that 

 Cepede, who stated that the supposed macronucleus of Kofoidella could 

 be demonstrated (by Maupas) only after treatment with acetic acid, 

 was referring instead to the trophic mass. 



The greater part of the Astomata inhabit the intestine of Oligochaeta. 

 In the table of distribution given by Cheissin (1930), records are given 

 of 69 species in the intestine of Oligochaeta, and of 41 elsewhere. Among 

 the latter, omitting Kofoidella and Chroniidina, the affinities of which 

 are doubtful, there are 36 species, and 12 of them occur in polychaetes 

 and in the coelom and gonads of oligochaetes. Heidenreich (1935) 

 added 11 species in the intestine of oligochaetes, and Beers (1938a) 

 added one. With about 75 percent of the known species in the intestine 

 of oligochaetes and polychaetes, and the affinities of many of those found 

 elsewhere doubtful, we may correctly consider the Astomata to have a 

 close ecological relationship to that group of animal hosts. 



Cheissin (1930), examining invertebrates of Lake Baikal for Asto- 

 mata, found none in many Turbellaria, molluscs, and polychaetes, and 

 only a few amphipods had Anoplophrya in the body cavity. Of 24 species 

 of oligochaetes examined, all the Lumbriculidae and most of the others 



