DAMPING OFF. 



249 



ing camera lucida drawings. After making several sketches of 

 desired objects one zoosporangium was discovered emitting the 

 protoplasmic vesicle preparatory to the differentiation of the 

 zoospores. When the eye first fell upon it the object was in the 

 phase represented by Fig. 18. Soon the protoplasm had all passed 

 through the short tube and was collected in a rounded vesicle at 

 the end. There was a slight differentiation of the protoplasm at 

 the time of the passage, but it was little marked. The differenti- 

 ation became more and more marked showing that the mass was 

 dividing into ten to twelve polygonal bodies. The surface of the 

 forming zoospore next the wall of the vesicle, or the periphery, is 

 the longer, and at the middle of the outer surface of the object 

 there soon appears a depression which gives each a curved appear- 

 ance. This form becomes more and more marked and now move- 

 ment begins, which first appears as a kneading of the entire mass, 

 and as they become more and more sharply differentiated each 

 young zoospore produces an oscillatory movement with its center 

 nearly stationary, the movement of course much restricted by the 

 surrounding vesicle. As they assume more distinctly the curved 

 appearance there is developed from each end of the zoospore a 

 cilium by the lashing of which the movement becomes more vio- 

 lent and results soon in the release of the swarmers when they 

 suddenly dart away. 



The movement is now a complex one. The oscillatory move- 

 ment is more marked with a tendency in many cases to produce 

 figure of 8 cycles, which is combined with a jerky progressive 

 movement in the direction of the longitudinal axis. Frequently 

 when they come in contact with some object larger in size, they 

 simulate to some extent the movements of a paramsecium along 

 some object in the water. 



The form of the mature zoospore is broadly fusoid, inequilateral 

 with pointed ends which terminate in a long cilium. After five 

 to ten minutes the movement of the swarm spores becomes slower 

 and finally it nearly ceases and the body undergoes plastic move- 

 ments resembling somewhat that of an amoeba as represented in 

 Fig. 24. At first this amoeboid movement is irregular but after a 

 few minutes it assumes a definite character which tends to cut 

 the organism into two parts. This progresses until complete 



