246 



BIOLOGY OF THE PROTOZOA 



from tlieir capsules, or introduced naked into the blood by some 

 intermediate host. They make their way to the definitive site of 

 parasitism, penetrate into cells and begin their development. In 

 the simpler gregarines only the young stages are passed in such host 

 cells and growth is not accompanied by any marked structural 

 differentiations. In the polycystid gregarines the parasite never 

 becomes entirely detached from its host cell until it is fully mature 

 and de-differentiation begun by the loss of the attaching organ 

 (epimerite). With its growth the body becomes differentiated into 

 an anterior chamber (protomerite) and a nucleus-holding posterior 

 chamber (deutomerite) and in the different species these three 

 portions of the cell become variously ornamented and specialized. 

 The epimerite particularly becomes modified in different ways that 

 are useful for purposes of anchorage. It may be a mere ball of 



Fig. 122. — Development of a polycystid grcgarine (schematic). (After Wasielewsky.) 



protoplasm as in Gregarina longa; a spade-shaped structure as in 

 Pileocephalus herri; a long knobbed proboscis either simple or pro- 

 vided with spines as in Stylorhi/iirhus lougicollis or Geniorhi/uchus 

 monnieri; or there may be many finger-form processes as in Echino- 

 viera hisjnda or thread-like processes as in Pterocephalus giardi. 

 In CoryceUa annata it becomes a single crown of hooks; in Beloides 

 firmiis hooks combined with a lone spine. While these epimerites 

 serve primarily for attachment, they also serve, in some cases at 

 least, as food-getting organs which they take at the expense of the 

 host. In Py.xinia moehiuszi the epimerite forms a long haustoria-like 

 process which extends through the epithelial cell of the gut and 

 into the blood lacunie of the submucosa (Fig. 93, p. 190) and in 

 Htylorhynclnis longicollis a canal is said to extend from the tip of the 

 epimerite through the primite and into the deutomerite of the 



