254 PROTOZOA 



suit, namely a 1:1 ratio of synclones of type B to synclones of 

 type C, Jennings reported 39 type B and none type C. The clue 

 to this exceptional result, in my opinion, is found in Jennings' 

 paper of 1941 which states that clone Lo 12, which was the type 

 C parent in the cross just mentioned, self-differentiated into types 

 C and B. On my hypothesis, the production of type B to the 

 virtual exclusion of other alternatives is a direct consequence of 

 mixture of cytoplasm between two mates, one of which had the 

 B cytoplasmic differentiator in highest concentration and the 

 other of which had it in second highest concentration, as indi- 

 cated by the type to which it could differentiate. 



In like manner, the occasional production of synclones differing 

 in mating type from either parent can be explained. These new 

 types often correspond to the second most concentrated cyto- 

 plasmic differentiator in one or the other or both parent clones, 

 as inferred from the type to which the parent self-differentiates. 

 Although this information is available for only a minority of the 

 parents reported upon by Jennings, in these cases the agreement 

 with expectation is on the whole impressive. However, there are 

 also a few instances of apparent disagreement. The outstanding 

 exception appears in one of the five crosses of mating types B and 

 D. This yielded a 1:1 ratio of A to D instead of B to D. Since the 

 B parent self-differentiated into C and the D parent arose by self- 

 differentiation in a B clone, my hypothesis leads to the expecta- 

 tion of an excess of B progeny, whereas in fact B progeny were 

 totally lacking. However, it is to be noted in this case that the D 

 parent was derived from an inbred ancestor which had for a few 

 generations repeatedly differentiated only into A and D, the B 

 arising as a late exception (Jennings, 1941). Here then is a pos- 

 sible case of a less probable and stable cytoplasmic state revert- 

 ing to a more probable and stable equilibrium. In view of the 

 obvious complexities of the general system, involving a fourfold 

 steady state system acted upon by genie and environmental fac- 

 tors, I am of the opinion that an apparent exception of the sort 

 just mentioned is not serious enough to invalidate the hypothesis. 

 What is now needed is a number of experimental tests directed 

 specifically toward disentangling the various components of the 



