History of the Theory of Heredity. 43 



productive organs of a caterpillar are already formed 

 before it leaves the egg. During its life in the egg, and 

 as a caterpillar, caterpillar-nuclein is formed in its germi- 

 nal cell-material. During the pupa stage pupa-nuclein 

 is stored up in its reproductive elements, and finally, 

 when it becomes a butterfly, butterfly-nuclein is stored 

 up. The ripe egg and the ripe male cell therefore con- 

 tain nuclein of three kinds, caterpillar-nuclein, pupa- 

 nuclein, and butterfly-nuclein." 



It will be seen that Jager's hypothesis is, in a certain 

 sense midway between evolution and epigenesis. He 

 holds that at first both the ovum and the male-cell are 

 unspecialized (entseelt) ; that they exist in the very 

 young embryo as embryonic ova or spermatozoa, and 

 that, as the embryo grows up, the reproductive cells 

 gradually become specialized by the assimilation of soul- 

 stuff, which is thrown off by the decomposition of 

 albumen in various parts of the body of *the growing 

 organism, and penetrating to the embryonic ova and 

 spermatozoa is assimilated by them, so that when the 

 animal becomes sexually mature, the cells of its repro- 

 ductive organs contain all the "soul-stuff" necessary to 

 produce a new organism like the parent. 



The statement which I have given is a free translation 

 of Jiiger's outline of his theory, and I think it may be 

 regarded as a fair exposition of his views. 



A fatal objection to his hypothesis is found in the 

 fjict that where a parent gives birth to young before it 

 has reached full maturity and before it has acquired all 

 t'ie characteristics of the species, the young neverthe- 

 less inherit these characteristics. The young which are 

 born by a Cycedomia larva inherit all the characteristics 

 of the full-grown adult insect, and a bull may transmit 

 to female children the good milking qualities of his 



