BERTRAMIA KIKKMAXI. 9 



With reference to the technique employed, it phoukl be 

 mentioned that the rotifers were fixed witli liot corrosive 

 sublimate solution ; ^ they were then carefully imbedded in 

 paraffin, and serial sections of 4i ^ in thickness were cut. 

 The sections were stained with iron-hasmatoxylin or Delafield, 

 followed by orange, eosin, or fuchsin, Flemniing's solution 

 was employed on two occasions, but the parasite becomes 

 intensely blackened with this reagent. 



The trophozoite grows and the number of nuclei increases 

 by karyokinesis. It is rather remarkable that in the younger 

 stages, if not later, all the nuclei in the trophozoite are 

 approximately in the same condition at the same time ; that 

 is, they are either all in the resting condition or all are 

 undergoing karyokinesis. This phenomenon would seem to 

 demonstrate the controlling action of the general cytoplasm 

 on the nuclei. 



The individual shown in section in fig. 2 contained about 

 six nuclei, and all of these were in a state of division. In 

 the process of karyokinesis the nuclear membrane gradually 

 disappears, and the chromatin becomes concentrated around 

 the circumference of the karyosonie (fig. 17, 1-3). The chro- 

 matin now divides into two granular sheets (4), which become 

 associated with two vesicles, formed apparently by the 

 division of the original karyosome, and are connected 

 together by achromatic fibres (5). The chromatic plate 

 extends over the surface of the vesicle (6), and, finally, the 

 chromatic substance becomes uniformly dispersed (7). In 

 fig. 17 (8) the nuclear membrane is being separated off from 

 the nucleus, and ultimately the karyosome diminishes very 

 considerably in size (9). In fig. 4 it is seen that all the 

 nuclei are preparing for division ; the nuclear membrane has 

 disappeared, and the chromatin lias become concentrated 

 around the periphery of the karyosome. In fig. 6 the con- 

 dition is shown where the nuclear membrane is reappearing. 



' A half-saturated solution of corrosive sublimate in 30 per cent, 

 spirit with 1| per cent, acetic acid. 



