EFFECTS OF AMPHIMIXIS ON ONTOGENY 293 



fact, it is expressly stated as regards the ^ otter sheep,' that 

 the offspring of the first ram ' closely resembled either the 

 mother sheep of the ordinary breed, or the ram ' ; and this 

 statement is in correspondence with the theory. Those sperma- 

 tozoa of the ram which contained the dominant group of idants 

 preponderated over the group of idants of the egg-cell, and an 

 'otter sheep' thus resulted; while those which contained the 

 subsidiary group of idants could only tend to produce an 

 ordinary sheep of the ancestral breed. 



A greater ' force of heredity' is also spoken of in the sense of 

 the prepotency of one race over another. According to Darwin, 

 the short-horn race of cattle seems to possess a particularly 

 marked power of transmission in contrast to other races ; and 

 this power is more marked in the pouter pigeon than in the fan- 

 tail, so that when these two races are crossed, the characters of 

 the pouter preponderate in the offspring. This preponderance of 

 one race over the other must be due to the same causes as those 

 which produce a much greater resemblance to one of the parents 

 in the case of plant-hybrids, which were discussed in another 

 section of this chapter. In both cases the preponderance may 

 be due to the presence of a larger number of idants, of ids, or 

 possibly even of biophors only, in the individual determinants. 



5. Summary of Chapter IX 



It may be advisable before proceeding further to give a short 

 summary of the results arrived at in the presenC chapter, and to 

 test the soundness of the assumption on which they are based. 



According to my view, the co-operation of the hereditary 

 substances of the two parents in the fertilised egg depends on 

 the presence in each parental germ-plasm of a large number 

 of units, and not of a single one. These units or ids are, 

 moreover, not all similar to one another in the case of each 

 parent, and although in iiorinal sexual reproduction they all 

 contain homologous determinants, they exhibit slight individual 

 differences. The differences between the ids of the two parents 

 need not in anv case be greater than those existinij between the 

 ids of the father or the mother alone ; it may, indeed, happen 

 that individual ids derived from both parents may be similar to 

 one another, and this is more likely to be the case the oftener 

 inter-breeding has taken place in previous generations. 



