624 FAMILY: CHILOMASTIGIDiE 



Kofoid and Swezy (1920) have given another interpretation of the 

 structure of the cytostomal cleft and blepharoplasts (Fig. 69). According 

 to them, the cytostome is an elongate aperture at the bottom of the cleft. 

 It is described as having the shape of the outline of a dumb-bell and sup- 

 ported by a fibre running completely round its margin. This fibre, as 

 also those found on the margins of the cleft itself, are said to originate 

 from one of the blepharoplasts. Of the latter, the left-hand one, which 

 turns round the posterior margin of the cleft, is called the peristomal 

 fibre and the other one the parabasal. As regards the blepharoplasts, 

 Kofoid and Swezy describe three which are united with one another by 

 various fibres called rhizoplasts, and with a granule on the nuclear mem- 

 brane which they call the centrosome. There seems little ground for 

 homologizing one of the marginal fibres with the parabasal bodies of other 

 flagellates, while the interpretation of the group of blepharoplasts is open 

 to question, especially as Belar (1921a) has published a description of the 

 structure of Chilomastix aulastomi of the leech {Aulastomum gulo), which 

 agrees e^ntirely with the account given above as far as the blepharoplasts 

 and cytostomal apparatus are concerned. 



The method of multiplication of C. rnesnili is undoubtedly by longitu- 

 dinal fission after division of the nucleus. Though the writer has seen 

 isolated stages of this process, it has not been followed in detail. The 

 longitudinal fission of C. aulastomi has been described by Belaf (1921o), 

 and it may be presumed that the division of C. mesnili will be very similar 

 (Fig. 257). Apparently, the cytostomal cleft and its fibres vanish, and a 

 single granule appears in place of the group of blepharoplasts, which 

 may be supposed to have become more closely packed together. This 

 granule is on the surface of the nuclear membrane, and it divides into two. 

 The two granules then take up positions at opposite poles of the nucleus, 

 and an intranuclear spindle is formed between them. The nucleus, which 

 retains its membrane, then moves to a more central position, and the 

 chromatin of the nucleus becomes arranged at the equator of the spindle 

 in the form of a plate of chromosomes. Two daughter plates are formed 

 by division of the chromosomes, and these move to opposite poles of the 

 spindle. Meanwhile, new flagella begin to grow out from the two granules, 

 which then subdivide into the several blepharoplasts. The elongated 

 nucleus is finally divided at its centre, and the daughter nuclei assume 

 the characters of the nucleus of the adult flagellate. Two new cyto- 

 stomal clefts and the other structures associated with them are formed. 

 The body of the flagellate now divides by constriction, and two flagellates 

 result. 



C. mesnili is often found in the stool in the encysted condition. The 

 cysts, which were first described and figured by Prowazek and Werner 



