MODES OF SEXUAL REPRODUCTION IN PROTOZOA 535 



formed directly from chromatin granules within the primary nucleus, 

 which, prior to this stage, had divided repeatedly until about 70 are 

 present. These secondary nuclei next fuse 2 by 2 in the cytoplasm 

 and give rise to spore mother cells (sporoblasts), of which there may 

 be as many as 250 w r ithin one parent organism, while at least one of 

 the primary nuclei remains unused and finally degenerates in the cell. 

 In Amoeba proteus, therefore, in autogamous fertilization the organ- 

 ism does not form one spore-mother cell (sporoblast), but many. 



2. Endogamy. In the mode of fertilization known as endogamy the 

 cell protoplasm breaks down into a number of portions, each one of 

 which receives some nuclear material. After the division of the proto- 

 plasm has taken place two of the distinct and separated masses fuse, 

 and around the two united gametes, now known as a copula, a spore 

 wall is formed. 



3. Exogamy. When two cells from different ancestors unite and 

 become completely fused the process is known as exogamy. This 

 method is very much like reproduction in higher metazoic animals, 

 where the male and female germ cells become fused to form a new 

 cell. The copulating protozoan cells may be perfectly alike (isogamy), 

 or they may be different in type (anisogamy). In the latter case, in 

 which two cells different in morphology become united, one can be 

 likened to the male and the other to the female germ cells of metazoa. 

 These germ cells of protozoa are called gametes. Budding is inti- 

 mately associated with conjugation, the buds are supplied with 

 chromatin, and they often subsequently become the conjugating 

 gametes. Budding, however, differs from spore formation. In the 

 former case the mother organism which gives off the buds continues 

 to live, while in spore formation the mother cell breaks up into spores 

 and ceases to exist. 



Spore Formation. In some protozoa, particularly in many flagellata, 

 this follows conjugation of two similar cells (isogamy). These 

 similar cells, after having united, form a common cyst, and the proto- 

 plasm in the interior of the latter becomes split into a great many 

 very small flagellated organisms. Among the class of protozoa called 

 sporozoa there are two types of spore formation. The spores formed 

 after fertilization are supplied with a firm protecting covering, and 

 they are able to exist outside of the body of the animal in which they 

 are parasitic as mature organisms. The spores formed asexually 

 have no such protecting envelope, and cannot live outside of their 

 host. Since the spores formed under such different circumstances 

 differ so much in their biologic properties, they have been distinguished 

 as sporozoites, those formed after fertilization, and merozoites, those 

 formed in an asexual manner. The former, can carry the infection 

 or disease from one host to another; the latter can only carry it 

 from one part of the infected host to another, but they cannot enter 

 the outside world. 



The term sporoblast designates the mother cell in which the sporo- 



