198 GEORGE W. TANNREUTHER. 



ing egg (double shelled) is represented in Fig. 3. The outer 

 shell membrane is external to the vitelline membrane and is 

 formed by a secretion from the uterus. The inner protective 

 membrane is formed from the cytoplasm within the vitelline 

 membrane. Fig. 4 represents the single-shelled resting egg, 

 which contains less yolk than the former. Two polar bodies 

 are formed in either case. The female parthenogenetic egg 

 (Fig. 5) is free from yolk and has a single polar body. The male 

 egg (Fig. 6) with the exception of the two polar bodies is in- 

 distinguishable from the female parthenogenetic egg. The cyto- 

 plasmic content of the above eggs from the standpoint of quantity 

 is about the same. 



Impregnation of the male-producing female brings about a new 

 condition in the formation and growth of the resting egg. The 

 vitellarium instead of remaining transparent as in the formation 

 of the parthenogenetic male and female eggs, becomes filled with 

 numerous spherical yolk bodies, which pass directly from the 

 vitellarium into the growing resting egg (Fig. I, r.eg). These 

 yolk-filled eggs are very dark, and unless fertilization occurs 

 further development stops after maturation. The eggs deter- 

 iorate and do not give rise to males as advocated by some of the 

 investigators on rotifers. The growth period of the female, 

 male and resting eggs with the passage of cytoplasmic granules 

 or yolk bodies from the vitellarium into the growing eggs, as 

 well as the maturation stages can be demonstrated under the 

 microscope in the living individual, the entire process- requires 

 about one hour. In this particular rotifer there can be no 

 question as to the structural differences in the male and the 

 resting eggs. The male eggs are always transparent, free from 

 yolk and incapable of being fertilized. Whether the male and 

 the resting eggs are the same or not before their growth period 

 begins in the ovary of the male-producing females I am unable 

 to say. There is a possibility of two distinct kinds of ova being 

 present: the one which normally becomes the male egg, the 

 other which requires impregnation before the growth period 

 begins in the formation of the resting egg. The ova that become 

 resting eggs never begin their growth unless impregnation occurs. 



