REPRODUCTION 51 



Plasmotomy. In certain Myxosporidia which inhabit organ- 

 cavities of the host fish, the multinucleate trophozoite has been 

 found to divide into two or more smaller, still multinucleate 

 bodies (Fig. 23). Doflein called this process plasmotomy. A 

 similar division is also noted in some Mycetozoa and occasion- 

 ally in Protociliata. 



Colony formation. When the division is repeated without 

 complete separation of the daughter individuals, various types 

 of colonies are produced. Based upon the arrangement of the 

 component individuals, these are usually placed under three 

 types: catenoid, arboroid, and spheroid. 



Catenoid (linear) colony. The daughter individuals are 

 attached endwise, forming a chain of several individuals. 

 Examples: the astomous ciliate, Haptophrya, and the dino- 

 flagellate, Ceratium. 



Arboroid (dendritic) colony. The daughter individuals re- 

 main connected with one another through attachment to stalks 

 or tests, producing a tree-like appearance. Examples: Dino- 

 bryon, Hyalobryon, Hydrurus (Fig. 31), Phalansterium (Fig. 

 45), Anthophysa (Fig. 55), Epistylis (Fig. 170), Carchesium 

 (Fig. 169), etc. 



Spheroid colony. The individuals are embedded in a gelatin- 

 ous matrix which is more or less rounded. Examples: Volvox, 

 Eudorina, Pleodorlna (Fig. 39), Syncrypta, Uroglena, Uro- 

 glenopsis (Fig. 30). Some are rosette-form, as in Gonium (Fig. 

 38) ; others are plate-form, as in Platydorina (Fig. 38). 



The gregaloid colony, which also is sometimes spoken of is a 

 group of individuals of one and the same species, usually of 

 Sarcodina, which become attached to one another by means of 

 pseudopodia. Such a colony can hardly be said to be due to 

 incomplete division of the parent body. 



Sexual Reproduction 



Some Protozoa reproduce themselves in a manner compar- 

 able to the sexual reproduction which occurs universally in the 

 Metazoa. Complete fusion of two gametes is here called copula- 

 tion and is to be seen in various groups. A temporary union of 

 two individuals for the exchange of nuclear material is desig- 

 nated as conjugation and is common among the Ciliophora. 



