394 C. W. MITCHELL AND J. H. POWERS 



from which they were started. The frequent outburst, within 

 certain Hnes, of the mutational tendency in the early generations, 

 which we explained in our former paper as probably due to quali- 

 tative nutritional change, we now see may well be due to inherited 

 high potential, with or without the special food stimulus. 



Indirectly too, the question of the percentage of male produc- 

 tion in different lines meets with a much needed additional expla- 

 nation. Male production, as we showed in our previous paper, 

 requires as its first and most fundamental condition, a state of 

 high potential. It thus follows naturally that strains originating 

 from resting eggs produced by parents in which this high potential 

 had been built up by special nutrition, or had been inherited 

 parthenogenetically, should become at once strains producing 

 many males; whereas, conversely, strains from resting eggs 

 dropped by parents of low potential inherit and maintain this 

 same inner condition, and while perfectly healthy, produce under 

 normal conditions few males. 



. In regard to the work of others upon the rotifer Hydatina, we 

 find that Punnett, Whitney, and ShuU, all in one way or another 

 emphasize the fact of races or strains in their material. These 

 strains of Hydatina show no morphological differences but con- 

 trast with each other in regard to number of males produced or in 

 regard to the general rate of parthenogenetic reproduction. Both 

 Shull and Whitney have also shown that the qualities of their 

 strains may be transmitted through the resting egg. We believe, 

 however, that in no case have they traced their strains to a 

 definite origin or shown that any quality induced by a known 

 agent became hereditary. Some of the work upon Hydatina 

 produces the general impression of a species, split up into what one 

 might be tempted to call 'elementary' strains, akin, in their fixity 

 if not in their morphological differences, to Jennings' races of 

 Paramecia; other portions of their work suggest, on the other hand, 

 that these strains are less fixed and in some cases arise while the 

 animals are under experimental observation. We hope that our 

 work may throw some light upon the method of their origin, on 

 their varying degrees of stability, and upon their frequent assump- 

 tion of a hereditary character. 



