468 H. H. NEWMAN 



than those normal to either strain or species. I am incUned to 

 interpret the speeding up of the developmental process in these 

 hybrids as the result of the introduction by the sperm of a for- 

 eign enzjone, which produces abnormally rapid dissociations in 

 the egg materials, and in this way hastens the processes of metab- 

 olism and development. Whatever be the chemical explanation 

 of the acceleration the fact remains that at a very early period, 

 certainly long before the end of cleavage, the hybrid eggs are 

 developing more rapidly than the pure bred ones. This can be 

 detected without the use of any refinement of method and should 

 be obvious at a very much earlier period if the methods pre- 

 viously used by the writer (Newman '10) were employed. If 

 anyone has abundant time and patience he might readily demon- 

 strate an acceleration in the first cleavages, but the writer has 

 foresworn any further attempts of this character as involving 

 labor incommensurate with the reward involved. 



Next in point of developmental success are the crosses between 

 the eggs either of F. diaphanus or of F. heteroclitus and the 

 sperm of F. ma j alls. Although the hybrids herewith treated 

 develop successfully and produce a fair percentage of vigorous 

 larvae they go much more slowly than the controls. It is also 

 to be noted that the hybrids between F. heteroclitus 9 X F. 

 majalis d" are much more viable than those between F. diaphanus 

 9 X F. majalis cf. 

 An interesting commentary upon the generalization of Moenk- 

 haus that foreign sperm always has a deleterious influence upon 

 the development of the egg, resulting in retardation of develop- 

 ment, is to be had from a study of the chart including figures 9 

 to 20. Here the developmental rates of eggs of F. diaphanus, 

 fertilized by three species of Fundulus sperm are shown in three 

 parallel vertical columns, the middle column showing the control 

 (pure F, diaphanus) that on the left F. diaphanus eggs fertilized 

 with F. majalis sperm, and that on the right eggs of F. diaphanus 

 fertilized with F. heteroclitus sperm. It will be readily noted 

 that the effects of the two types of foreign sperm are of an exactly 

 opposite character, the one producing marked retardation and 

 the other equally marked acceleration. No theory depending 



