392 GEORGE W. TANNREUTHER 



The January and March cycles were not studied very exten- 

 sively. The studies proper were begun with the May cycle, 

 1916, in tracing out the cell lineage. The adults are extremely 

 transparent, and by holding them in any desired position under 

 a supported cover-slip the cleavage of the individual cells can 

 be traced step by step. Two distinct kinds of adult females 

 exist, which are structurally similar as far as can be determined 

 under a magnification of 100 to 150 diameters. The one repro- 

 duces females parthenogenetically, and the other males parthen- 

 ogenetically or resting eggs, which carried the cycle of one period 

 to their next reappearance. The resting eggs pass through their 

 early stages of cleavage before deposition. There are, however, 

 two kinds of resting eggs: a very thin-shelled one, with a single 

 shell membrane, and a thick-shelled egg, with a double shell 

 membrane. The thin-shelled egg develops with the same 

 rapidity as the parthenogenetically produced individuals and 

 hatches out immediately after deposition. Two polar bodies 

 are formed in each kind of resting egg, which do not develop 

 unless fertilized. 



Females and resting eggs or females and males are never 

 produced by the same individual. The parthenogenetically 

 produced males and females are sexually mature at birth. The 

 uterus of the young females often contains embryos in the late 

 cleavage stages at the time of their birth. The two kinds are 

 practically the same size at birth. Copulation occurs almost 

 immediately after the birth of the males. The male may copu- 

 late with either kind of female. The uterus and the oviduct of 

 the parthenogenetic producing female often contain sperm, but 

 neither males nor resting eggs are produced by this particular 

 individual. On the other hand, the uterus and oviduct of the 

 male-producing parent may contain an abundance of sperm, and 

 yet produce males only, or again, they may produce both males 

 and resting eggs. There is no definite sequence in the production 

 of males and resting eggs by the same parent. A single male 

 may be produced and all the remaining become resting eggs, or 

 vice versa. Or, on the other hand, it is not unusual to find the 

 two alternating. The following is a good example : the sequence 



