214 



PROTOZOA. 



ectosarc, produced by circular or spiral muscle fibrillaj. These 

 muscles explain the peristaltic motion and the occasional sharp 

 bending of the body, but not the peculiar gliding motion like that 

 of diatoms by which locomotion is usually effected. This is 



pm 



din. 



Fig. 155.— Development of Gregarina blattarum. I, conjugation ; II, A~C, a cyst in 

 transformation into pseudonavicellie; III, ^, apseudonavicella greatly enlarged; 

 B, same with sickle-formed sporozoites; cu, cuticle; dm, deutomerite; ck. ecto- 

 sarc; en, entosarc; it, nucleus; pm, protomerite; p?i, pseudonavicella?; rk, re- 

 sidual body; sk, sickle-form sporozoites. 



explained by the view that the gregarines secrete stifE gelatinous 

 threads from the posterior end, and the elongation of these forces 

 the body forward. 



In many gregarines (Polycystidaj) the body is divided by a cir- 

 cular incision into a smaller anterior jiart, the protomerite, and a 

 larger deutomerite. Interiuilly this division is marked by a bridge 

 of ectosarc across the entosarc. The vesionhir nucleus (there is 

 but one in any gregarine) lies in the deutomerite. An epimerite — 

 a structure connected with the peculiar type of jiarasitism — occurs 

 in many species. All gregarines are parasitic in youth inside of 

 cells. They later leave tliese. but m:iny remain for a long time 

 with a process of the protomerite imbedded in the cells. This 

 process — the ejiimerite — is provided with threads or hooks for 



