THE MASTIGOPHORA 135 



from two to five androgonidia, but there may be one hundred andro- 

 gonidia in V. minor while there are only eight gynogonidia. Each 

 female cell becomes at first flask-shaped, then withdraws inside of the 

 colony and becomes a mature egg. The male cell, at the beginning 

 about three times the size of the sterile cells, soon begins to divide in 

 one plane until a bundle of from sixty-four to one hundred and twenty- 

 eight flagellated, spindle-formed elements results. These, the sperma- 

 tozoids, gather around the egg-cells, which are fertilized exactly as in 

 higher animals or plants. Fertilization takes place while the egg is 

 still in the parent colony ; the copula forms two membranes about 

 itself, while the color changes from green to orange. After a consid- 

 erable resting period, the egg undergoes regular cleavage, forming the 

 adult colony, in which, even before the embryo leaves the egg, the 

 cells are differentiated into somatic cells and parthenogonidia. After 

 these cleavage stages the outer cyst wall is ruptured and the young 

 colony swims out. 



G. INTER-RELATIONS OF THE MASTIGOPHORA 



Transitional forms between the Mastigophora and the Sarcodina 

 show how closely the two classes are related. The development, 

 both in Sarcodina and in Mastigophora, throws little or no light upon 

 the question as to the more primitive nature of one or the other. 

 While many Sarcodina have flagellated swarm-spores, many Flagel- 

 lidia have amoeboid spores, and even in the same species both amoe- 

 boid and flagellated swarm-spores are formed at the same time 

 (Acant/iocystis Schaudinn, see Fig. 53, F). 



The most primitive forms of Flagellidia suggest the long-disputed 

 question over the boundary-line between animals and plants. 1 Un- 

 questionably, the most primitive flagellates are those forms which, 

 while actively motile, possess chromatophores and chlorophyl, and 

 are able to make their own food, or which, like the bacteria, can sup- 

 port themselves upon simpler substances than proteid. The living 

 flagellates which come closest to these primitive types are the monads, 

 while the Choanoflagellida are probably not far removed. Klebs ('93) 

 takes the ground that the collar-like process of the Choanoflagellida 

 is not a sufficient taxonomic differential save for ordinal distinctions, 

 and recent zoologists are inclined to accept this view. 



Stein, Biitschli, and Bergh have been the most active in formulat- 

 ing views as to the origin of the Dinoflagellidia, although none of 

 these is wholly satisfactory. Some authors derive them from the 

 Phytoflagellida directly (Haeckel), others place them as a group of the 



1 Cf. p. 22. 



