MV( KTOZOA AND PkoTI <)MY.\ A 



27 



arising an gametes and the zygotes formed by their iusion give rise to 

 the conspicuous syncytial stage partly by simple growth accompanied 

 by mitosis, partly by numbers of them crowding together and undergoing 

 fusion. 



Under the name PROTEOMYXA are frequently grouped together a 

 numlu-r <>l interesting genera of rather uncertain affinities. Two members 

 of the group may be mentioned as being of special intm-st. Pseudospora 

 is i'reijurmly encountered in the laboratory during the examination of 

 I'obox (sec below, p. 38). It has the appearance of a small Amoeba 

 (Kig. 10, A), and is to be seen creeping about in the Volvox colonies and 

 devouring the cell-individuals. In a bad epidemic of Pseudospora the 

 Volvox colonies may be almost entirely destroyed by its ravages. The 



FIG. 10. 



Pseudospora (from M. Robertson). A, creeping ; B, swimming ; C, floating phase, c.v, Con- 

 tractile vacuole ; /, food ; f.v, food-vacuole ; n, nucleus. 



special feature, apart from its frequent occurrence, which makes it worthy 

 of mention here is its remarkable polymorphism. On occasion it will 

 take on an elongated form of body with two flagella at one end by the 

 movements of which it swims actively through the water (Fig. 10, B). 

 At other times (Fig. 10, C) it will become spherical with fine tapering 

 pseudopodia radiating from it, and superficially placed .contractile 

 vacuoles, looking precisely as if it were a member of the group Heliozoa 

 to be described below. Pseudospora thus illustrates particularly clearly, 

 within the compass of its own life-history, three different physiological 

 types of body which occur independently of one another very commonly 

 in the Protozoa and which are associated respectively with a creeping, 

 a swimming, and a floating habit of life. 



Plasmodiophora the other genus is of interest as being the cause of 

 the important disease of Cabbages and Turnips called Finger and Toe 



