ETJGREGABINARIA. 53 



in pairs, and both produce an equal number of gametes, which 

 are usually equal in size though not always in character, 

 since those arising from one gametocyte may behave as male 

 gametes and those from the other as female gametes. Con- 

 jugation thus takes place between similar or dissimilar gametes 

 {isogamy or anisogamy) . In a small group, however, schizogony 

 takes place as well as sexual reproduction, and the order is 

 divided into two suborders on this basis. Thus : 



No schizogony Suborder Eugregarinaria Doflein, p. 53. 



Schizogony takes place . . . Suborder Schizogregarinaria Leger, p. 111. 



I. Suborder EUGREGARINARIA Doflein, 1901. 



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

 garines, which are usually parasites of Arthropods or Annelids. 

 The sporocyst, after gaining entrance to a suitable host, 

 germinates and sets free the sporozoites, which enter the 

 epithehal cells of the digestive tract. There they grow large 

 and protrude from the host-cells, remaining attached to them 

 by an organ of attachment, called the epimerite, of varied form. 

 These trophozoites sooner or later become detached from the 

 ceUs of the host and move about in the lumen of the gut, 

 where they are usually encountered as large and vermiform 

 bodies exhibiting a ghding movement. In one group, the 

 Sbptata, the main body is divided into two parts, which are 

 distinctly marked off from each other by an ectoplasmic 

 septum. The smaller anterior part is known as the protomerite, 

 and the larger posterior part the deutomerite. The latter 

 contains a single nucleus. In the other group, the Haplocyta, 

 the body is not divided by a septum, and consists of a single 

 chamber. In this latter group the sporozoites penetrate the waU 

 of the gut and enter the body- cavity, forming cysts on the 

 coelomic side of the intestinal waU, or develop as free forms 

 inside the seminal vesicles or other parts of the body-cavity. 



The trophozoites increase in size and are then known as 

 gametocytes ; these then encyst in pairs. Within the cyst- 

 membrane each gametocyte gives rise to a large number of 

 gametes, which may be isogamous or anisogamous. Each of 

 the gametes formed from one gametocyte unites with one 

 formed from the other, and a large number of zygotes are 

 the result. Each zygote becomes surrounded by a resistant 

 membrane (oocyst or sporocyst), and its contents produce 

 usually eight sporozoites. 



The suborder is divided as follows : — 



[kester, p. 54. 



Trophozoite single-chambered Legion Haplocyta Lan- 



Trophozoite divided by an ectoplasmic [p. 89. 



septum Legion Septata Lankester, 



