ASPLANCHNA EBBESBORNII (rOTIFER) 393 



was as follows: two resting eggs, one male, one resting egg, one 

 male, one resting egg, one male. 



In case of the female which produces the resting eggs the 

 vitellarium undergoes a marked change after impregnation. 

 The yolk spherules become larger and more abundant and give 

 the vitellarium a very dark color. The yolk is first produced at 

 the point where the oviduct takes its origin. This process 

 continues until the vitellarium is completely filled with yolk. 

 Where males and resting eggs are produced by the same parent, 

 the yolk is produced at intervals just before the resting egg 

 begins its growth in the ovary. The male eggs are free from the 

 dark yolk and remain transparent. Impregnation has no effect 

 on the vitellarium of the female-producing individual in the 

 production of yolk. Figures 7 to 11 show the single thin-shelled 

 and the double thick-shelled resting eggs. In figure 12 the 

 spermatozoa are shown in different stages of development. 



In many instances the sperm of the sexually mature male 

 (before birth) would escape from the testis and become deposited 

 in the uterus of the parent and bring about the production of 

 resting eggs. In other cases the male was little more than a 

 large sperm sac. The male embryos developed normally until 

 the early differentiation of the reproductive organs. At this 

 stage of development all of the cleavage cells, except those directly 

 concerned in the production of the sperm, ceased dividing, took 

 on a vesicular appearance, gradually deteriorated, and functioned 

 as food for the developing sperm. The sperm, when . m.ature, 

 escaped through the egg membrane into the lumen of the uterus. 

 This condition accounts, to some extent, for the few free-swim- 

 ming males in the cultures. 



The males are structurally degenerate at birth. The digestive 

 tract is very rudimentary (figs. 5 and 6) and never opens to the 

 exterior. The males are very short-lived, and few free-swimming 

 individuals are present at any one time. The males do not 

 increase in size after birth (figs. 5 and 6). On the other hand, 

 the females increase to at least four to six times their size at the 

 time of birth (fig. 1). The embryology of the male and the 

 female developing individual is practically the same throughout 



