TRANSITIONS IN MORPHOLOGICAL CHARACTERS 93 



EXPERIMENTS 



Observations on a 7?iass culture 



In order first to observe the development of the species under 

 normal conditions a mass culture was reared from resting eggs. 

 These eggs were transferred from the pond water in which they 

 had been produced to fresh tap water. Many had hatched by 

 September 28, or in about six days. These were all small saccates 

 and rapidly gave rise to large numbers of the same type. By 

 October 10 the entire culture had changed to the humped form, 

 males had been produced, and resting eggs were present. This 

 culture was conducted for a considerable period and displayed the 

 typical development of the species.' 



Observations on the development of the saccate type in 

 isolation culture 



On October 4 resting eggs were again taken from the same supply 

 as the above and placed singly in a series of twenty watch glasses 

 each containing the culture medium. By October 7 five of these 

 had hatched. One was chosen as the parent of a pedigree series 

 termed A . Later, still more of the eggs hatched and on the thir- 

 teenth, a newly bom saccate individual was isolated to become 

 the parent of a pedigree series D. In series A were bred twenty- 

 six generations, and in D one hundred and eight, the purpose being 

 to determine the effect of isolation upon individuals in a genetic 

 series. The results obtained from all of A and from fifty genera- 

 tions of D are recorded in table 1. Briefly stated they are: first, 

 a marked persistence and uniformity of the saccate type, and, 

 second, an almost total absence of males. The saccate type did 

 not give rise to the humped form, a fact contrary to all observa- 

 tions in general cultures. This was wholly unlooked for. The 

 water in both general and isolation cultures was taken from the 

 same source; the food introduced was identical, and the tempera- 

 ture conditions very similar; yet the two results are markedly at 

 variance. 



