GREGARINIDA 



also in the gut of Tunicata and Insecta (fig. 60) and in the seminal 



vesicles of Annelida. In the polycystid gregarines a single septum only 



is present as a rule, and thus the body presents two portions : (i) an 



anterior portion termed the protomerite ; (2) a 



posterior, larger portion, known as the deuto- 



merite, which generally contains the nucleus. 



The protomerite is often modified anteriorly 



to form an organ of attachment, termed the 



epimerite (fig. 61), which is developed from the 



pointed rostrum of the sporozoite or primary 



infecting young gregarine. The structure of 



the epimerite may be complicated, being pro- 

 vided with hooks, spines, knobs, and other 



appendages. An extension of the polycystid 



condition is seen in Tceuiocystis inira Leger 



(from the dipteran larva, Ccratopogon solstitial is), 



whose body shows a number of partitions, 



giving the organism a superficial resemblance 



to a tapeworm. 



The ectoplasm of a gregarine exhibits three 



layers : (i) An epicyte (cuticle) externally of 



which the epimerite is composed ; (2) a 



sarcocyte which forms the septa if present ; 



(3) the deeper myocyte layer containing con- 

 tractile elements in the form of fibrils or threads 



termed myonemes (fig. 62). 



The endoplasm is fluid and granular, con- 

 taining many enclosures, which are of the nature of reserve food 



materials. They consist of fat drop- 

 ^ L y lets or of paraglycogen, and give 

 the organisms an opaque appear- 

 ance. Lithocystis contains crystals 

 of calcium oxalate in its endoplasm. 

 Many gregarines are capable of 

 active movements, though they do not 

 possess obvious locomotor organs: 

 The movement is of a smooth, 

 gliding character and two sug- 

 gestions have been put forward to 

 explain it. According to Schewiakoff, 

 a gelatinous substance is secreted be- 

 tween the layers of the ectoplasm. 

 This is extruded posteriorly and thus 



the animal is pushed forward. On the other hand, Crawley considers 



that the movements are produced by contractions of the myonemes. 



FIG. 61. Xyphorhynchus 

 firmus with epimerite in 

 intestinal epithelial cell of 

 host. (After Leger.) 



FIG. 62. Grearina munieri (from 

 the beetle, Chrysomela hcemoptera). Sec- 

 tion through surface layers. Cu, cuticle ; 

 , ectoplasm proper ; G, gelatinous 

 layer ; My, myonemes in myocyte layer, 

 x 1500. (After Schewiakoff.) 



