Development of Rotifer vulgaris. 139 



studies from day to day. I cultivated great quantities of these 

 animals in two small aquaria filled with rain-water. Swarm- 

 spores of Alga3 served as their food. Early in the morning (at 

 4 or 5 o'clock) I constantly found, seated at the margin of the 

 aquarium, colonies of the size of a pin's head, which, on micro- 

 scopic examination, proved to consist of 30-40 individuals. 

 Among them were to be seen 50-60 eggs, either freshly depo- 

 sited or already in course of development, which one of course 

 has to make use of at once. That so many observers of Rota- 

 toria have failed (as appears from the memoirs on the subject) 

 in obtaining eggs just deposited is due simply to the fact that 

 they did not get up early enough. So far as I can judge, the 

 deposition of eggs in Philodina roseola takes place only very 

 rarely during the later hours of the morning, and not at all 

 in the afternoon. This condition has its analogue among the 

 lower forms of plants. To the botanist it is well known that 

 the conjugation of many Algas takes place only in the earliest 

 hours of daylight. 



While the mature egg of Philodina roseola is still in the 

 body-cavity of its parent, the germinal vesicle always lies at 

 that pole which is turned towards the anal aperture. I was 

 never able to detect a germinal spot in Philodina roseola. 



Upon the first stages of development I have to state what 

 follows. In the deposited egg the germinal vesicle imme- 

 diately disappears, and, just as in Botifer, the vitelline 

 granules accumulate around a central point, so that a peri- 

 pheral layer of protoplasm, with but few granules, makes its 

 appearance in the egg. Gradually, however, the contents of 

 the latter become homogeneous, but only for a time, for very 

 soon the yelk becomes clearer at two neighbouring points of 

 the long axis of the egg, and between these is produced the 

 first groove, by which the contents of the egg are divided into 

 two unequal parts. In proportion as the deepening of the 

 groove proceeds, the nuclei of the first two segments also 

 appear with more distinct contours. That the first segmen- 

 tation-nucleus is developed by gemmation from the nucleus of 

 the egg I have several times directly observed in Philodina 

 roseola. For the elucidation of this I refer to fig. 4, in which 

 four consecutive stages of the process of gemination in ques- 

 tion are represented. At the commencement of the gemmation 

 the true viscous nuclear substance within the fine envelope 

 containing it performs amoeboid movements (stage 1, fig. 4). 

 But within a few minutes the budding daughter-nucleus 

 distinctly appears (stage 2). Immediately aft.er its production 

 this divides into two or three equivalent structures (stage 3), 

 and I have even observed a case in which the whole nucleus 



