A. FRANKLIN SHULL. 



Dried for a Long Period. No experiment with control, in- 

 volving a longer period of desiccation than four weeks, was per- 

 formed; but that some eggs could withstand longer desiccation 

 was shown. One lot of 344 cross-fertilized eggs and another of 

 IOO inbred eggs, all from sources not used in the experiments 

 described in this paper, were kept in dried condition from June 

 29 to March 23, or about nine months, when they were remois- 

 tened. In about three weeks thereafter three eggs of the first 

 group and one of the second hatched. 



All these eggs simply rested on the bottom of a watch glass 

 when dried. It is not improbable that when the eggs, on drying, 

 are supported by mud or sand they may remain desiccated longer 

 and still hatch when remoistened. But even in mud the possible 

 period of desiccation is not indefinitely long; for out of a lot of 

 fertilized eggs in dried mud I have secured numerous young roti- 

 fers after three months of desiccation, but no eggs hatched from 

 this lot after two years. 



SUMMARY AND DISCUSSION. 



In former papers (Shull, 1913, 1915) the inheritance of size of 

 parthenogenetic eggs, the time of development of parthenoge- 

 netic eggs, the place of laying parthenogenetic eggs (surface film 

 or bottom), the viability of fertilized eggs (proportion that hatch), 

 and the contractility of foot muscles was described. In this 

 paper is shown to what extent these inherited characters may 

 have been modified by such external agencies as temperature, 

 oxygen, and desiccation. 



It was found that if the water in which the rotifers live was 

 exposed to an atmosphere containing more than the usual pro- 

 portion of oxygen, a greater proportion of the eggs were laid at 

 the bottom of the vessel. Under ordinary conditions the rotifers 

 probably come to the surface because of the greater quantity of 

 dissolved oxygen there. Those lines which normally lay their 

 eggs mostly at the bottom probably either require less oxygen 

 or get their oxygen more easily than lines which lay their eggs 

 at the surface film. The hereditary character involved may 

 therefore be the oxygen requirement or the permeability to 

 oxygen. 



