394 GEORGE W. TANNREUTHER 



the different stages of development. One polar body is formed 

 in the female egg, while in all others two polar bodies are formed. 

 The individuals hatching from the resting eggs are always 

 parthenogenetic females. But the next generation is of two 

 kinds, one producing females parthenogenetically and the other 

 producing males parthenogenetically or resting eggs. 



MATERIAL AND METHODS 



The rotifers were removed from the different cultures with a 

 pipette and placed in watch crystals. The excess water was 

 then removed and the fixing fluid added. Bouin's fluid gave 

 the best results. The animals were preserved in 70 per cent 

 alcohol until used. If allowed to stand indefinitely in alcohol 

 the individuals turn brown and are not very satisfactory for 

 study. For whole amounts Delafield's haematoxylin and eryth- 

 rosin were used. Either stain gave good results. The changes 

 from alcohol to xylol and from xylol to the mounting medium 

 must be made very gradually. A few drops of carbo-xylol and 

 clove oil will help considerably in the process. The cuticle is 

 very resistant and will cause considerable shrinkage and dis- 

 tortion if the change be made too quickly. The same caution 

 must be taken in clearing specimens that are to be imbedded 

 and sectioned. Iron-alum haematoxylin and erythrosin gave the 

 best results for sections. In the case of whole mounts, the cover- 

 slips should be supported. 



ORIGIN AND FORMATION OF OVUM 



The reproductive organs are composed of the vitellarium, 

 ovary proper, oviduct, and uterus. The uterus opens into the 

 urogenital sinus. The vitellarium is somewhat U-shaped (fig. 4), 

 very transparent when free from yolk, and contains many large 

 nuclei. The ovary (figs. 1 to 4) occupies a very small area at 

 the base of the vitellarium. 



Parthenogenetic ova : The ova are very small, and a single ovum 

 at regular intervals begins its growth. The contents of the 

 growing egg is derived directly from the vitellarium. The 



