THE SPOROZOA 159 



small one, which has all of the characteristics of a spermatozoon. In 

 the same year Simond worked out again the life-history of the Coc- 

 cidium of the rabbit and described a true copulation between the 

 microsporozoites. Schaudinn regards this, however, as an error, 

 holding that copulation takes place between one of the smaller forms 

 and an enlarged ordinary individual. 



Since then, the fact of fertilization, with the resulting formation of 

 sporozoites through spores, has been safely established for a number 

 of species by several different observers, the details alone differing 

 in the several cases. The microsporozoites thus are not true sporo- 

 zoites, but gametes having a sexual function. 



According to these various observations the life-history of the Coc- 

 cidiida may now be described as follows : the permanent cysts contain 

 spores, each of which contains sporozoites which are taken into the 

 digestive tract with the food. Here the cyst membrane bursts or is 

 dissolved, and the sporozoites are liberated. They penetrate the 

 epithelial cells and grow to the normal size of the adult. They then 

 undergo repeated nuclear division by a process which resembles frag- 

 mentation rather than mitosis (Schaudinn), or (possibly) in some cases 

 by binary division also (Labbe), and the nuclear parts wander out to 

 the periphery, where small portions of the cytoplasm form around 

 them and they are pinched off as minute germs which Simond called 

 merozoites. These differ in several important respects from the 

 sporozoites, but like them are capable of developing directly into new 

 adult parasites. This process, which Schaudinn calls schizogony, 

 leads to the increase of parasites within the host (Fig. 88, a-c). Dur- 

 ing development, some of these merozoites store up reserve nutriment 

 and form large ovoid cells, while others form the mother-cells of the 

 microsporozoites or spermatozoids, without storing up a reserved food 

 supply. The small forms, in some cases, are provided with flagella, 

 which were first made out by Leger and by Wasielewski. Fertiliza- 

 tion takes place in a manner almost identical with that of the Metazoa 

 (d-j}. In some cases a micropyle is formed in the egg through 

 which a spermatozoon can enter, and in all cases after one has 

 entered, a hard membrane corresponding to the vitelline membrane is 

 at once formed (). Complete fusion takes place between the nuclei, 

 and the cleavage nucleus divides by repeated mitosis to form spores. 



It is quite probable that the other cases of dimorphism, which have 

 been recorded from time to time, are instances of similar sex-differen- 

 tiation. The motile forms especially, which numerous observers 

 have recorded, will probably be found to be similar in function. 

 Laveran ('98), Bosc ('98), Sjobring ('97), Wasielewsky ('98), Sied- 

 lecki ('98), and others have recently described them in different 

 Coccidiida (Fig. 89). 



