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



these lines were very large and showed much vigor. This last 

 experiment with humped lines not only adds one more instance 

 of unbroken heredity through the resting egg, but is of interest in 

 that the stock was derived from series K rather than from /, 

 showing that the two series comport themselves quite alike in 

 this respect. The origin and conduct of the mass culture from 

 which K 2 was derived is perhaps of still more interest. It shows 

 that a single isolated parthenogenetic reversion to the saccate 

 type does not necessarily mean a permanent drop in potential 

 to the saccate level. Why, we can not say, but may easily con- 

 jecture that the isolated appearance of such saccates may have 

 been due to a somatic rather than a germinal influence. 



CONCLUSION 



We need hardly repeat, in resume, the main conclusion to which 

 these experiments lead: The hereditary transmission of induced 

 germinal modification through sexual as well as through parthe- 

 nogenetic generations. Certain minor aspects of the matter, how- 

 ever, need further accentuation. First, the unique fact that a 

 certain type or form when once induced (the humped form of 

 A. amphora) may in reality be transmitted with full force despite 

 an interruption of one or more generations (saccates from resting 

 eggs) in which this form is not expressed. Although the condi- 

 tions are totally different the phenomenon suggests that of reces- 

 sive and dominant characters. 



Second, it is worth while to accentuate the nature of the results 

 of sexual reproduction in this rotifer with regard to vitality and 

 variation. The limits of our experiments, it is true, are narrow, 

 as all of our series were begun with inbreeding. But within these 

 limits the results are definite and uniform. The union of gametes 

 has little if any influence upon the vitality of the race; it is true 

 that the resting eggs hatch irregularly but oi^ce hatched they show 

 the normal growth and reproductive energy of the strain from 

 which they are derived. There is no added vitality, no rejuvi- 

 nation. As to variation again, the results of fertilization seem 

 purely negative, excepting of course, the temporary return to 



