POLYTOMA 173 



recent and very trustworthy observers. On the other hand, the 

 same species has been seen to form a spherical cyst with a thin 

 envelope, inside which the protoplasm became divided into 

 several young forms, which emerge on rupture of the cyst. In 

 Bodo angustatus several individuals have been seen to come 

 together and fuse to form a plasmodium just as the amcebulae 

 of Badhamia fuse to form the plasmodium of that genus. The 

 plasmodium then forms a cyst wall and enters into a resting 

 stage. Any undigested food particles are extruded, and the 

 contents of the cyst divide into numerous small spores which 

 are set free in the shape of the parent form. A similar mode of 

 conjugation has been described in Bodo globosus; but it is 

 questionable whether the fusion of several individuals has any 

 importance, for in both species free swimming individuals may 

 encyst and form spores without any previous conjugation of two 

 individuals. Seeing that conjugation followed by encystment 

 and spore formation undoubtedly occurs in closely allied species, 

 there is good ground for accepting the account given for Bodo 

 saltans as correct in the main ; and the process as described in 

 this species is of importance, for not only do we find conjuga- 

 tion, but the conjugating individuals or gametes are in so far 

 dissimilar that one is anchored, the other free swimming ; and 

 we have here the first suggestion of a differentiation of sex, the 

 stationary form being perhaps comparable to a female the free 

 swimming form to a male gamete. 



Polytoma uvella is a flagellate found often in association 

 with Bodo in long standing infusions of organic matter. It is 

 slightly larger than Bodo, and of different shape, being almost 

 perfectly oval, with a pair of flagella of medium length projecting 

 from one of its ends. Both flagella are used equally in 

 swimming, and the organism darts with great rapidity through 

 the water, pursuing a more or less definite course. Whereas 

 the protoplasm of Bodo is naked, that of Polytoma is invested 

 by a delicate but distinct membrane or envelope. Usually the 

 protoplasmic body completely fills the cavity of the envelope, so 

 that the latter is difficult to see ; but if the organism is badly 

 nourished the protoplasm shrinks, and the envelope becomes 

 obvious. This fact shows that the envelope is not a differentia- 

 tion of the most external layer of protoplasm but a true 

 protective covering secreted by but distinct from the protoplasm. 



