CHAPTER XXIII 



ORDER 3 GREGARINIDA LANKESTER 



THE GREGARINIDA are chiefly coelozoic parasites in inverte- 

 brates, especially arthropods and annelids. They obtain 

 their nourishment from the host's organ-cavity through osmos- 

 is. The vast majority of the Gregarinida do not undergo schizo- 

 gony, or asexual reproduction, and the increase in number is 

 carried on solely by the sporogony following gametogony. In a 

 small group, however, schizogony takes place as well as sexual 

 reproduction and this is used as the basis for the division into 

 two suborders, as follows: 



No schizogony Suborder 1 Eugregarinina 



Schizogony takes place Suborder 2 Schizogregarinaria 



Suborder 1 Eugregarinina Doflein 



This suborder includes the majority of the so-called gre- 

 garines which are common parasites of arthropods. When the 

 spore gains entrance to a suitable host, it germinates and the 

 sporozoites emerge and enter the epithelial cells of the digestive 

 tract. There they grow large and protrude from the host cells 

 to which they are now attached by various cell-organs of 

 attachment. These trophozoites sooner or later become de- 

 tached from the host cells and move about in the lumen of the 

 gut. This stage is ordinarily most frequently encountered. It is 

 usually vermiform and large. The body which is covered by a 

 definite pellicle shows a clear differentiation into the ectoplasm 

 and endoplasm. The former contains myonemes which enable 

 the organism to undergo a gliding movement. In one group, 

 Acephalina, the body is of a single compartment, but in another 

 group, Cephalina, the body is divided into two compartments 

 which are separated from each other by an ectoplasmic septum. 

 The smaller anterior part is the protomerite and the larger 

 posterior part, the deutomerite, contains a single nucleus. The 

 protomerite may possess an attaching process with hooks or 

 other structures at its anterior end; this is called the epimerite. 



[291] 



