230 BIOLOGY: GENERAL AND MEDICAL 



circulate and be added to those in the stirp is granted, 

 and they explain the rare cases in which zebra marks 

 occur on the foal of a thoroughbred mare by a thorough- 

 bred horse, owing to the fact that the mare had pre- 

 viously born a mule to a zebra; but to have them circu- 

 late in such numbers and so constantly as the doctrine 

 of pangenesis implies would over-explain such cases." 



"Of the two groups of germs, the one consisting of 

 those that succeed in becoming developed and in form- 

 ing the bodily structure, and the other consisting of 

 those that remain continually latent, the latter vastly 

 preponderates in number." "We should expect the 

 latent germs to exercise a corresponding predominance 

 in matters of heredity, unless it can be shown that, on 

 the whole, the germ that is developed into a cell be- 

 comes thereby more fertile than if it had remained latent." 



The theory of the stirp transfers the hereditary 

 material from the somatic to the germinal cells. Con- 

 trasting his views with those of Darwin, the following 

 language is used by Galton: 



1. "There are cells and there are a great number of gemmules. 



2. "The cells multiply by self-division, and during this process 

 they throw off gemmules. (I look upon this process of throwing 

 off the gemmules to be of such minor importance as to have no 

 effect whatever upon the cases we have thus far considered. Its 

 existence is granted, but only as a subordinate process, to account 

 for the exceptional cases to be hereafter considered and not as 

 the primary process in heredity.) 



3. "The gemmules multiply by self-division, and any gemmule 

 admits under favorable circumstances of being developed into a 

 cell. (I look upon this as the primary process in heredity.) 



4. " The personal structure is formed by a process analogous to 

 the fertilization of each gemmule that becomes developed into a 

 cell by means of the partially developed cell that has preceded it in 

 the regular order of growth. (I look on it as due, first, to the 

 successive segmentations of the host of gemmules that are con- 

 tained in the newly fertilized ovum, owing to their mutual affinities 

 and repulsions; and, secondly, to the development of the dominant 

 or representative gemmules in each segmentation, the others 

 remaining dormant, and are called, for convenience, in the next 

 paragraph, the residue.) 



5. "The sexual elements are formed by aggregation out of the 

 gemmules, all of which are supposed to travel freely throughout 

 the body. (I look on the sexual elements as directly descended 



