96 PROTOZOA, 



The degenerate state of the conjugation appears to be of a similar 

 nature to the degenerate sexual process in certain low fungi, such as 

 Saprolegnia^ in each probably an effect of parasitism. In each case 

 there is a sort of imitation of the real process although the essential 

 interchange of nuclear material is absent. 



The sporocyst finally bursts and the coated spores are 

 set free out of the anus of the cockroach. Protected by 

 the hard coat these spores lie dormant till any 

 of them happen to be introduced with food 

 into the intestine of another cockroach. In this event the 

 spore-case bursts and its contents escape as a creeping 

 amoeboid nucleated mass of protoplasm. This works its 

 way into the epithelial cells of the cockroach's intestine 

 and there remains for some time. It is then termed an 

 intracellular parasite, living withifi the epithelial cell. 

 Here it grows and assumes the elongated form and other 

 characters of the adult. Contemporaneously it gradually 

 protrudes from the cell into the lumen of the intestine, 

 still attached by the anterior end with its cap. Finally it 

 becomes detached and lives free in the lumen or cavity of 

 the intestine. 



We may note that there is a definite limit to the number 

 of gregarines which can dwell in one cockroach, and when 

 this limit is reached the gregarines would perish with their 

 host. Hence the gregarines and all endoparasites must 

 at some time, if the species is to be maintained, migrate 

 and by some means reach a fresh host. This is not 

 essentially different from a sheep moving to fresh pasture 

 after having exhausted the previous one, but in the former 

 case the probabiHties of reaching the fresh scene of action 

 are infinitely less. The difficulties of the migration are 

 overcome in two ways : — Firstly, an enormous number of 

 the migrating units are produced just before the migration, 

 the number roughly corresponding to the probabilities of 

 survival ; secondly, the migrating units are protected for 

 their hazardous journey by hard coats or cases. In these 

 respects the gregarine is typical of endoparasites. (See also 

 Parasitism, Chapter IX.) 



