192 POPULAR SCIENCE MONTHLY. 



are ready to form spores. The nucleus divides repeatedly, and a 

 great number of buds are formed around the daughter nuclei (Fig. 

 2, l, c). These buds elongate from the periphery of the parent organ- 

 ism and radiate from it, like the spines of a sea urchin. When 

 fully developed, the spores, or, as they are technically known, the 

 merozoites, drop off the parent cell and work their way through the 

 fluids of the digestive tract until they come to the cells lining it, and 

 then, like the sporozoites, they penetrate the cells, grow at their 

 expense, and again reproduce spores as before (Fig 2, a to c). This 

 process thus tends to spread the disease among the cells of the digestive 

 tract in the one host, and it will be observed that the reproductive 

 process is not accompanied by the union of two gametes, as in the case 

 of Monocystis. Coccidium is thus distinguished from the latter in 

 having a method of asexiial multiplication leading to auto-infection. 

 This process, however, cannot continue indefinitely, and, after five or 

 six days, a method of sexual multiplication supervenes. The prelim- 

 inary stages of this process do not differ from the formation of the 

 merozoites, and similar buds are formed which break off' and penetrate 

 the epithelial cells as before. The further history, however, differs 

 markedly from that of the merozoite. Some of the resulting parasites 

 give rise to immense numbers of minute, active, thread-like buds, the 

 microgametes, which radiate from the parent cell like the merozoites 

 (h — j). Others do not form buds at all, but merely enlarge until they 

 are as large, or larger than, the ordinary full-grown parasites (d — f). 

 One of the small forms then fuses with a large form, in conjunction; 

 and the result, or copula, secretes a firm cyst about itself, and then 

 divides into spores (2, g). Each spore then secretes about itself a second 

 coating which becomes impregnated with calcareous matter, and, Avithin 

 this cyst, the cell divides into a small n,umber of sporozoites (1-). 

 In this condition the primary cysts are emptied to the outside, Avhere 

 they are ultimately taken up by some new host in whose digestive tract 

 the cysts are dissolved and the sj)orozoitcs liberated to renew the 

 cycle (Fig. 2, 0- 



It thus appears that, in Coccidium, the life cycle is more complicated 

 than in the gregarine, in having a period of asexual reproduction by 

 which auto-infection is accomplished, alternating with a period of 

 sexual multiplication during which the parasite is carried from one host 

 to another. Coccidium differs further from Monocystis in that 

 the conjugating gametes are sexually differentiated, the small, active 

 one, or microgamete, functions as the male cell, and the larger, quiescent 

 one, or macrogamete, as the female or egg cell, while in the gTCgarine, 

 on the other hand, the conjugating gaiuetes are of equal size. 



We may now consider the somewhat more complicated life cycle 

 of the malaria organism. The process of spore-formation of this para- 



