383 



sperm species is more rapid or slower than that of the egg species. Thus, 

 reference to Table 3, where Fundulus heteroclitus was the egg species and 

 Tautogolabrus adspersus was the male species, the rhythm of cleavage fol- 

 lows exactly that of Fundulus, although that of Tautogolabrus is very much 

 faster. The reciprocal shown in Table 4 shows that the rate again is that 

 of the egg species — Tautogolabrus. This is true all the way through, but 

 attention is called to the hybrids with Opsanus tau, where the cleavage 

 rhythm is relatively so extremely slow. (Page 373.) These facts are in 

 accord with many observations made by others, especially Driesch ('98) 

 on Echinoderms. Newman ('08, '10) obtained the same results in his 

 Fundulus heteroclitus^Fundulus majalis hybrids. Fischel ("06), on the 

 contrary, maintains that the influence of the sperm in some of the Echino- 

 derm hybrids, makes itself felt even in the first cleavage. It is important 

 to note, however, that such influence as he can detect is always to slow 

 the development. This is what I find everywhere, as will appear further 

 on, but I have not been able to detect it during the early cleavage stages. 

 This slowing of the developmental processes is to be looked upon as patho- 

 logical, a sort of incompatibility of the two germinal substances in such 

 cases as it occurs. If it is permissible, as some authors do, to speak of the 

 rhythm of cleavage as a character of the organism, then all my experiments 

 most clearly show that the rate of earlier cleavage of the embryo is unin- 

 fluenced by the sperm, and may be regarded as wholly determined by 

 the egg. 



In later cleavage and all subsequent stages, the influence of the 

 strange sperm becomes apparent in all the cases that I have carefully 

 watched. It should be said here that hybrids between the nearly related 

 species were not studied in this particular, but only those between the more 

 distant forms. The influence of the strange sperm was in every case to 

 retard development, usually to a marked degree, regardless of whether 

 the developmejital processes in the sperm species was much more rapid or 

 slower than in the egg species. Thus Tautogolabrus adspersus takes only 

 from twenty-four to thirty-six hours to hatch, while Fuudulus heteroclitus 

 takes from ten days to fourteen days, the hybrids, using Fundulus as the 

 egg species, are slower in their development than Fundulus itself. The 

 tendency, then, among fish hybrids obtained by combining distantly related 

 species, is to develop slower after their earlier cleavage stages, than the 

 egg species. It is, therefore, interesting to note Newtnan's result where 



