396 H. S. JENNINGS AND K. S. LASHLEY 



would be expected if the distribution of the 83 deaths had no 

 relation to the method of pairing? 



It is important to realize that these two ways of putting the 

 question are identical. The probabihty that 38 complete pairs 

 should survive is in this case the same as the probability that 28 

 complete pairs should die, and this is true in general. Therefore 

 we need deal explicitly with only one of these questions; the answer 

 we obtain will hold for both. This will be demonstrated later. 



Miss Cull ('07) appears to leave out of consideration all pairs 

 in which both members die, dealing only with those which survive. 

 At the end of a month, since 28 pairs out of the 93 had died out, it 

 follows that there were left representatives of but 65 pairs, and it 

 is only these 65 that she considers in summing up the evidence in 

 favor of sexual differentiation: 



It may be broadly stated that of the sixty-five pairs which I have 

 observed one conjugant either died or left a weak strain in which the 

 descendants were half as numerous and much less vigorous than those 



of the stronger ex-conjugant Here we have indications 



that one gamete gives up its vitality to and loses its identity in the egg 

 where its presence forms a stimulus to development analogous to the 

 rajeunissement and greater activity in cell division which follows con- 

 jugation. There is little reason to doubt that a physiological and per- 

 haps a physical difference exists between the two unicellular organisms 

 which unite in conjugation and a difference of the same nature as that 

 expressed morphologically in the case of Adelea ovata, where the male 

 gamete does not fuse with the female, but dies after delivering one of 

 its four pronuclei (pp. 88, 89). 



Now, even if we deal only with the survivors, as in our first 

 way of putting the question, we come to the same result as when 

 we deal only with those that die (as set forth above, and as will 

 be demonstrated later). But in any case, the results given in 

 my paper on the effects of conjugation ('13) show that there is 

 no justification for omitting the cases in which both members of 

 the pair die. Miss Cull did this apparently on the ground that 

 these were instances where conjugation was unsuccessful in pro- 

 ducing rejuvenescence, so that the animals died as they would 

 have done if there had been no conjugation. She says of the death 

 of these 28 pairs: ''These facts confirm Calkins' observation 



