REPRODUCTION OF PROTOZOA. loi 



is an incipiently sexual process ; it is the analogue of the 

 fertilisation of an ovum by a spermatozoon. 



It is one of the recurrent phases in the life-history of 

 some of the simplest Protozoa (Proteomyxa and Mycetozoa, 

 see p. 1 08), that a number of amoeboid units flow together 

 into a composite mass, which has been called a "Plasmod- 

 ium." 



It is known that more than two individual Gregarines 

 and other forms occasionally unite. To this the term 

 " multiple conjugation " has been applied. 



Commonest, however, is the union of two apparently 

 similar individuals, either permanently so that the two fuse 

 into one, or temporarily so that an exchange of material is 

 effected. Permanent conjugation has been observed in 

 several Rhizopods, Infusorians, and Gregarines. Temporary 

 conjugation is well known in not a few ciliated Infusorians, 

 and it is possible that a curious end-to-end union established 

 between certain Gregarines is of the same nature. 



Fourthly, there are some cases where one of the con- 

 jugating individuals is larger and less active than the other. 

 Thus in Voriicella, a small free-swimming form unites and 

 fuses completely with a stalked individual of normal size. To 

 call this " dimorphic conjugation " is hardly necessary, since 

 it is evidently equivalent to the fertilisation of a passive 

 ovum by an active spermatozoon, one of the well-known 

 characteristics of reproduction in the Metazoa. 



The conjugation of ciliated Infusorians, such as Paramx- 

 ciutn, has been studied with great care by Gruber, Maupas, 

 R. Hertwig, and others, and though their results are not 

 quite harmonious, the main facts are secure. In the ciliated 

 Infusorians there are two nuclear bodies, one large, the 

 other small. The smaller or micro-nucleus lies by the side of 

 the larger or macro-nucleus. The micro-nucleus divides into 

 parts, while the macro-nucleus degenerates. Two indivi- 

 dual Infusorians (A and B) lie side by side in close contact, 

 and a portion of the micro-nucleus of A passes into B, and 

 a portion of the micro-nucleus of B passes into A, or else 

 two portions of A and B simply come into very close 

 contact. An interchange of some sort takes place, the 

 conjugating individuals separate, a new micro-nucleus and 

 a new macro-nucleus are established in each. 



