132 



THE PROTOZOA 



complex nuclear changes. As in the Reticulariida and some Sporo 

 zoa, the chromatin is reduced to minute granules which are spread 

 throughout the cell, but in the Flagellidia they are so small that their 

 further history is not known. Not all forms, however, are of this 

 primitive type ; some, as for example Noctilnca miliaris, and some of 

 the Dinoflagellidia, undergo a complicated mitotic process which in 

 Noctiluca is repeated until five or six hundred spores are formed 



(Fig. 74)- 



The formation of spores or gametes may or may not be preceded 

 by the conjugation of individuals. In those species of Mastigophora 

 in which spore-formation is preceded by conjugation, a very interest- 

 ing series of forms may be 

 selected, showing the grad- 

 ual development of sex from 

 types in which there is a 

 union of individuals of sim- 

 ilar form, size, and, appar- 

 ently, of condition, to the 

 union of specially developed 

 male and female reproduc- 

 tive elements. Cienkowsky 

 ('56) was the first to observe 

 the fusion of similar monads, 

 but the most complete obser- 

 vations are those of Dallin- 

 ger and Drysdale ('73), who 

 watched the fusion of several 

 individuals of Bodo (Cerco- 

 monas) crassicaicda, the en- 

 cystment of the fused mass, 

 and the subsequent divisions of the plasm up to the formation of 

 an immense number of minute spores (Fig. 75). In another form 

 (yOikomonas Dallingeri~) similar spores are formed, but without the 

 preliminary fusion of two or more small individuals. The gametes 

 move about until they come in contact with the adult individuals with 

 which they fuse. The fused mass then encysts and finally breaks up 

 into minute spores. 



An advance toward sexual differentiation is seen in Pandorina 

 (Pringsheim, '69), where, after a long period of asexual reproduction 

 resulting in numerous colonies, the cells separate and begin to form 

 swarm-spores which may be of the same or of different size. These 

 spores then swim about until two of them meet and fuse by the color- 

 less ends into a common body (Fig. 76). Fusion may take place 

 between two small gametes, or between a large and a small one. 



Fig. 74. — Aocttluca miliaris Sur. 

 [Robin.] 



Spore-formation. 



