62 MULTIPLICATION OF PROTOZOA 



characters, and the other vegetative chromatin, which has to do with 

 the vegetative functions. Amongst the Plasmodroma and the Proto- 

 ciliata both kinds of chromatin are contained in one nucleus, and it is 

 supposed that the extrusion of chromatin material from the nuclei of 

 gametes, which has been described as taking place in certain instances, is 

 an expulsion of the vegetative chromatin in preparation for syngamy. 

 If this explanation is the correct one, it has to be admitted that after 

 syngamy the vegetative chromatin can be re-formed from the generative 

 chromatin, as illustrated by the formation of new macronuclei from the 

 micronuclei after syngamy in the Euciliata. The theory depends very 

 largely on an exact definition of what is and what is not chromatin, and 

 a correct interpretation of the various parts of the nucleus, about which 

 at the present time there is considerable difference of opinion. Dobell (1 925) 

 has described a condition of binuclearity in Aggregata (see p. 873). 



MULTIPLICATION AMONGST THE PROTOZOA. 



Multiplication takes place by a process of binary fission or gemmation 

 in which an organism divides into two daughter organisms after division 

 of the nucleus, or by a process of multiple segmentation, which is generally 

 known as schizogony amongst the Sporozoa, where it occurs most typically, 

 after a number of nuclei have been formed by repeated divisions. 



BINARY FISSION. — The process of binary fission may give rise to 

 daughter forms which are equal in size (equal binary fissions), or to forms 

 w^hich are unequal in size (unequal binary fission). When there is a 

 marked difference in size between the two, the process is known as budding 

 or gemmation, a method of multiplication which is seen typically amongst 

 the attached Euciliata (Peritrichida and Suctoria), where a large form buds 

 off a small ciliated embryo which does not itself reproduce till it has grown 

 to the adult form. 



In the case of amoebae which have globular bodies, binary fission is 

 effected by the body becoming elongated and a constriction forming 

 around the middle of the body (Fig. 36). This deepens till the amoeba 

 is divided into two parts. The daughter forms may not divide again till 

 they have grown to the size of the parent. On the other hand, they may 

 divide before growth is complete, with the result that increasingly small 

 individuals are produced. If they divide only after they have grown to 

 a size larger than that of the parent, then larger forms are gradually 

 produced. In the case of the amoebae it is evidently impossible to state 

 that division takes place in any one plane, except that it occurs in a plane 

 at right angles to the axis occupied by the elongate dividing nucleus. 



Directly it becomes possible to orientate an organism, and state that 

 it possesses an anterior and posterior end and a dorsal and a ventral 



