100 PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



of a new individual, while merozoites have a shorter life to run and a 

 lessened vitality (see Chapter III). 



Merozoite formation is best illustrated by the coccidia, a group of 

 cell-infesting sporozoa, and the genus adelea is an interesting type, 

 because it combines asexual reproduction with sexually differentiated 

 organisms. A word here as to the significance of this fact. In the 

 sporozoa, both in the gregarinida and the coccidiidia, the cycle ends 

 with the formation of sexually differentiated reproductive bodies, one of 

 which is larger, corresponding to an egg cell, the other very minute and 

 similar to a spermatozoon; the former is called a macrogamete, the 

 latter a microgamete. The mother cells of these gametes are not 

 visibly different in many cases, and it is impossible to tell whether a 

 given cell will produce one or the other. In some cases there is a slight 

 difference either in size, or in possession or absence of granules, or in 

 the make-up of the nucleus. These differences do not go far back, as 

 a rule, and in the ordinary rim, male and female cannot be distin- 

 guished. In adelea and a number of other forms, however, the sexual 

 differences do go back almost to the fertilized cell, and it is possible to 

 distinguish any given cell as female or male. The formation of 

 asexual reproductive elements, or merozoites, in these different 

 parents is the same, and begins with the division of the nucleus into 

 as many parts as there will be merozoites, in adelea usually twelve to 

 sixteen. After their formation they occupy a peculiar and character- 

 istic position, being rolled together like staves of a barrel, or like the 

 segments of an orange, a peculiar arrangement which has given rise 

 to the name cor'ps en barillet, while the term eimerian cyst is also used 

 designate the parent membrane cyst where they are formed (Fig. 20, A). 



The sporozoites differ but little from the merozoites when they are 

 deprived of their protecting cases. After fertilization of the macro- 

 gamete, which will be described in a later chapter, the nucleus of an 

 ordinary coccidian, such as Coccidium schubcrgi, for example, divides 

 twice and the protoplasm surrounds them in equal masses; these are 

 the sporoblasts. The nucleus of each sporoblast then divides again, 

 while the protoplasm secretes a sporoblast membrane, one of the pro- 

 tecting coats of the sporozoites. The second division of the nucleus 

 in each sporoblast provides the nuclei of the sporozoites, two develop- 

 ing in each sporoblast. The germs are then protected by the sporo- 

 blast membrane, and by a membrane which is secreted by the original 

 cell, and with this double safeguard the germs of the organism are 

 thrown to the outside, where no further development takes place until 

 the sporocysts are swallowed by some new host (Fig. 36, /). 



The variations in these processes of merozoite and sporozoite forma- 

 tion are legion, and they are of great importance economically, as well 

 as interesting biologically, but their description belongs rather to the 

 special chapters dealing with protozoan diseases. 



