THE GREGARINES AND COCCIDIA 



327 



As a rule, in such cases there is but a single septum, which divides 

 the body into two parts termed respectively protomerite and deuto- 

 merite (Figs. 7, 142) ; but in the curious genus Tceniocystis (Leger, 

 616) there are a number of septa, 

 giving the parasite a superficial 

 resemblance to a segmented worm. 



The body of a gregarine consists 

 typically of distinct ectoplasm and endo- 

 plasm. The ectoplasm may be further 

 differentiated into three layers : an ex- 

 ternal cuticle or epicyte, a middle layer 

 or sarcocyte, and a deeper contractile 

 layer or myocyte containing myonemes 

 (Fig. 29. p. 58). The epimerite, with 

 its hooks and processes, is derived from 

 the epicyte ; the septa, if present, from 

 the sarcocyte. The endoplasm is usually 

 extremely granular, and contains great 

 quantities of stored-up food material in 

 reserve for the reproductive processes ; 

 chief amongst these substances are para- 

 glycogen - spherules, extremely charac- 

 teristic of these parasites. 



A remarkable feature of gregarines is 

 the power possessed, by many species, of 

 gliding forward, often at a great pace, 

 without any visible organs of locomotion. 

 Two explanations have been given of 

 these movements: (1) by Schewiakoff, 

 that they are due to extrusion of 

 gelatinous fibres from the hinder end of 

 the body, secreted between the epicyte 

 and sarcocyte ; (2) by Crawley. that the 

 movements are produced by contrac- 

 tions of the myonemes which are only 

 present in motile forms. In motionless 

 forms the ectoplasm is very thin, and 

 consists of epicyte alone. 



The nucleus of a gregarine is usually 

 very large, spherical, and vesicular in 

 type, with one or more distinct karyo- 

 somes. It is typically single, except hi FIG. 142. Examples of gregarines 

 the cases of precocious association men- in the " cephalont >! condition, 

 tioned belowexceptions, however, which 



* ( _ 



are only apparent, since in such cases 

 the gregarine represents in reality two 

 individuals fused into one. In the 

 septate forms the nucleus lies in the 



deutomerite normally. In Pterocephalus (Nina), however, a second nucleus, 

 which appears to be of transitory nature and to take no share in the repro- 

 ductive processes, has been discovered in the protomerite (Leger andDuboscq, 

 621). The nucleus-like body observed by Siedlecki in Lankesteria ascidice, 

 and by Wenyon (84) in L. culicis, occurring at the point of contact of the two 

 associated sporonts in the cyst, is perhaps a body of similar nature. The 

 nucleus of CallyntrocMamys phronimce is remarkable for being surrounded 

 by a halo composed of radiating processes, each a thin tubular evagination 



Actinocephalus digacanthus ; 

 B, Stylorhynchus longicollis. ep., 

 Epimerite ; pr., protomerite ; d., 

 deutomerite. After Schneider. 



