470 H. H. NEWMAN 



ever, is based on an almost diametrically opposite assumption 

 and is suggested by a series of experiments which I performed 

 with the idea of testing the effects upon development of freshness 

 and staleness of the germinal products. Similar results were 

 obtained several times, but sometimes what seemed to be the 

 same treatment gave different results. Eggs of F. heteroclitus 

 were fertilized with the sperm of F. majalis which had been kept 

 alive for about twenty minutes in 45 per cent sea-water, a con- 

 centration that greatly prolongs the life of these spermatozoa. 

 A very small percentage of eggs cleaved, but these-developed 

 normally and showed scarcely any trace of the paternal influ- 

 ence either in rate of development or in details of inheritance; 

 while the control strain, from the same batch of eggs fertilized 

 at the same time by more sperm obtained fresh from the same 

 male, showed the usual retardation in development and the 

 typical hybrid characters described here and subsequently. It 

 might then be concluded that, when the sperm is so stale that 

 it is barely able to initiate development in the egg, it plays a 

 role equivalent to that of the reagents that produce artificial 

 parthenogenesis, but is unable to take part in the differentiation 

 of hereditary characters. According to this view, the most active 

 sperms might have the most deleterious effects upon the egg mate- 

 rials of another species and give rise to serious incompatibilities 

 whose result is more or less pronounced abnormality, and cessation 

 of development; while the sperms that have lost some of their vigor 

 are less likely to disturb the developmental rhythm of the egg and 

 thus more likely to give normal embryos. 



b. Unsuccessful crosses 



It will have been noted that, although the reciprocal crosses 

 produce viable larvae, the hybrids between F. majalis 9 and F. 

 diaphanus cf and those between F. majalis 9 X F. heteroclitus 

 cf never produce larvae, since they never truly hatch. They 

 may live for weeks within the egg membrane but gradually suc- 

 cumb to anemia. The difficulty is almost certainly one involv- 

 ing retarded or partial yolk assimilation, since in the final stages 



