10 ERNEST WAEKEN. 



It will be noticed that all the nuclei in the trophozoite are in 

 the same stage at the same time. 



The trophozoite is able to reproduce by fission, and also 

 by a kind of budding. In fig. 5 (3 and 7) the trophozoite is 

 about to divide by binary fission. The Y-shaped ti'ophozoites 

 break up into three individuals. These phenomena have 

 been termed plasmotomy by Doflein, and although their 

 occurrence has been denied, they undoubtedly take place in 

 Bertramia kirkmani. An individual undergoing binai'y 

 fission is shown in section in fig. o, and it should be noticed 

 that the fission appears to be in no way directly connected 

 with the division bf the nuclei. Plasmotomy appears to be 

 only possible in the early stages of growth. 



The trophozoites grow into sausage-shaped bodies, which 

 may be equal to half the length or more of the entire rotifer. 

 The whole of the body-cavity of the rotifer may become 

 almost completely choked with these bodies, which vary very 

 much in size, and I have counted as many as forty individuals 

 in one host. 



As the trophozoite grows the protoplasm becomes charged 

 with refringent grannies, which at first tend to be confined 

 towards the centre ; but later on they extend throughout its 

 substance, and the hyaline protoplasm ultimately becomes 

 densely granular and opaque. 



Fig. 7 shows a portion of an individual which has nearly 

 completed its growth : the protoplasm is fairly granular and 

 the nuclei are numerous. In a lai'ge individual the number 

 of nuclei would be considerably over a hundred. It may be 

 noticed that the nuclei of the adult trophozoite are only about 

 half the size of those of the youngest trophozoite (c f. fig. 1 

 and fig. 7). 



The trophozoite next passes into the spore-producing stage. 

 In fig. 8 it will be seen that the cytoplasm contains very 

 numerous large, refringent granules. The karyosome has 

 apparently become swollen, so as to occupy the whole area of 

 the nucleus, and the nuclear membrane is not distinct from 

 it (c f . figs. 17, 7, 8). The nucleus is now surrounded by an 



