THE MYCETOZOA 



nucleus. A contractile vacuole has, meanwhile, appeared in each 

 daughter- cell, at a point remote from the plane of division, and 

 each develops a flagellum after separation is complete (15). It is 

 probable that many generations of swarm- cells produced in this 

 manner succeed one another during this stage of the life-history. 



When the zoospores are 

 treated by Heidenhain's hae- 

 matoxylin method, or with 

 picrocarmine, a reticulum comes 

 into view in the nucleus, and 

 the nucleolus takes a dark stain. 



FIG. 3. 



Three stages in tlie division of 

 zoospore of Itetimilaria lycnjtenlon. 

 x 1000. (After A. Lister, 17.) 



FIG. 4. 



Xoospores of llatlhnniia panicen, 

 stained, x 0.00. 



The nucleus is sometimes round (Fig. 4, b), but more often it is- 

 pyriform, being drawn out towards the base of the flagellum 

 (Fig. 4, a). The protoplasm intervening between the nucleus and 

 the flagellum is differentiated from the rest, and takes a darker 

 stain. It thus forms a more or less bell-shaped investment of the 

 former, the contour of which is most clearly seen in specimens- 

 which have assumed an amoeboid shape without retracting the 

 flagellum (Fig. 4, c). 



Plenge (21) first called attention to this bell-shaped structure; and 

 Jahn (11), who has recently investigated it afresh, considers that it is- 

 part of the spindle formed in nuclear division when the zoospore divided, 

 and remaining in connection with the daughter nucleus. Jalm's figures 

 illustrating this point are very clear, but he does not explain how the 

 structure is formed in the zoospore prior to its first division. 



In this and also in the succeeding stage a resting phase may 

 intervene between periods of activity. In it the flagellum and 

 pseudopodia are withdrawn, and the protoplasmic body rounding 

 itself into a sphere secretes a hyaline cyst-wall. These cysts are 

 known as microcysts. The formation of microcysts may be readily 

 induced by allowing a cultivation of swarm-cells to dry up, but 

 dryness is not a necessary condition for their production, for they 

 are formed in water, and some are present in almost every cultivation 

 of swarm-cells. 



(b) The Amoebula. 



After remaining for a period of uncertain duration in the stage 

 of their life-history in which the dominant form is that of the free- 



