536 BIOLOGY OF THE PROTOZOA 



and maintains that the force generated by the secretion of slime is 

 sufficient to send the organism forward on the principle of a sky- 

 rocket. 



The majority of observers (Leidy, Luhe, Paehler, Shellack, Dogiel, 

 Cognetti, Roskin and Levinson, etc.) maintain that myonemes 

 alone are responsible for the movements of various types of greg- 

 arines, the latest view (Roskin and Levinson, 1929) referring 

 them to the activities of the circular and longitudinal myonemes 

 in much the same way as an earthworm moves through contraction 

 of its longitudinal and circular musculature. The nature of the 

 remarkable threads in Zygocystis zonata is not clear. Bowling 

 (1931) observed the thickening of the threads both in living and in 

 fixed material, but whether this indicates a cause or a result of 

 movement is not evident. 



Apart from changes in shape due to movements form changes 

 due to development and differentiation are highly characteristic, 

 particularly of the septate gregarines. In all gregarines the early 

 stages in the development of the sporozoite are cytozoic parasites. 

 After a period of growth the partly developed gregarine escapes 

 from the host cell and from that time on lives as a celozoic parasite 

 (Haplocyta). In septate gregarines, however, while the bulk of the 

 young parasite extends into the lumen of the organ, a small portion 

 remains as an anchor in the protoplasm of the host cell. This 

 anchoring part then develops into a specialized structure known as 

 the epimerite which is a characteristic morphological element of the 

 majority of Eugregarinida occurring here and there among the 

 Haplocyta (I)iplocystidae, Schaudinnellidae and Rhynchocystidae). 



The character of the epimerite is a diagnostic feature of impor- 

 tance in the classification of gregarines. Its development into a 

 long intracellular filament is well shown in Leger and Duboscq's 

 illustration of Pyxinia moebiuszi (Fig. 103, p. 201). In other cases it 

 is a mere knob or button within the membrane of the host cell 

 (Stenophoridae), or a knob with recurved hooks as in Corycella, 

 Hoplorhynchus, Sciadophorus, etc. in short it is a morphological 

 feature of great diversity. 



In these septate forms the body is further characterized by the 

 division into chambers (polycystid gregarines of earlier authors) 

 due to the ingrowth of the sarcocyte to form a posterior portion 

 bearing the nucleus and an anterior portion from which the epi- 

 merite arises. When the organism approaches maturity these cham- 

 bers separate from the epimerite, leaving it in the host cell, and 

 as gamonts become free in the lumen. In some rare cases the 

 anterior chamber is also cast off with the epimerite (Genus Schnei- 

 deria), and it frequently becomes a continuous part with the 

 epimerite. 



Some forms, notably the Monocystidae, may be highly metabolic; 



