H. M. FucHS 229 



comparisons, of making the experiments under such conditions that 

 comparisons are strictly possible. In previous work, the results of which 

 have depended on the percentages of eggs fertilized under different 

 conditions, the method of experimentation has in general been for from 

 exact. This is often the case in Echinoderm hybridization work — and 

 numerous other examples might be cited, but the investigation which 

 particularly interests us here is that of T. H. Morgan on fertilization in 

 Ciona (9, 10, 11). 



A considerable part of the work of this investigator was concerned 

 with the question as to whether the eggs of all individuals are capable 

 of being fertilized by the sperm of all other individuals. This is a 

 problem of peculiar interest, especially in view of recent work on self- 

 sterility in plants. It is far from being an easy point to settle, since 

 the difficulty of making up the sperm -suspensions of the different 

 individuals to be compared of even approximately equal concentrations 

 is great. That this equal strength of the different sperm-suspensions 

 is an absolutely necessary datum for interpreting the results is shown 

 by the fact that in making cross-fertilizations even small differences in 

 sperm-concentration produce large variations in the percentages of eggs 

 fertilized. Morgan's method was to select five or six individuals, make 

 all the possible reciprocal fertilizations between them, and then compare 

 the percentages of eggs fertilized in the different crosses. It is stated 

 (9, p. 148) that "The sperm, a, of the first individual was then taken 

 out and put into a small amount of water. It was then distributed to 

 one set of eggs from each of the other individuals, B, C, D, E; then the 

 sperm of B was taken out and applied to another set of eggs." It is 

 not stated, however, whether sperm b was of nearly the same concentra- 

 tion as sperm a ; nor is there any mention as to whether the eggs and 

 sperm were thoroughly mixed before fertilization, and with one another 

 at the moment of insemination. The observation is made, however 

 (10, p. 321), that in all cases enough sperm was probably used to fertilize 

 all the eggs capable of uniting with that sperm. In the first series (9) 

 several of the combinations were made twice in the same experiment, 

 but frequently gave very divergent results. Thus in Exp XIII, Ea 

 (i.e. E eggs with a sperm) gave first 100 °/„ and then 85 7o of fertilized 

 eggs. In Ex. XIV, Ea gave 0% and 4>°l^: Ae 0% and 100%. In 

 Exp. XV, Ea gave 2 7„ and 7„ : De 90 7, and 100 7„ : Ae % and 

 100 7„. In Exp. XVI, Ea 5°/, and 70 7„: De 100 7„ and 30 7„: Ae 

 75 7o ^■nd 100 7o- It seems extremely probable that these divergencies 

 are due to inexact experimentation, although Morgan suggests (10, 



