xix HEREDITY 369 



embryonic and undifferentiated, retaining the many- 

 sidedness of the original egg-cell, preserving intact and 

 uniformly the potential qualities abcvyz. They form 

 the future reproductive cells let us say the eggs. 



Now when these eggs are liberated, with the original 

 qualities abcxyz unchanged, having retained a continuous 

 protoplasmic tradition with the parent ovum, they are 

 evidently in almost the same position as that was. There- 

 fore they develop into the same kind of organism. Given 

 the same kinds of protoplasmic change or metabolism 

 occurring in the same protoplasmic material, the same 

 inherent qualities, the same conditions of birth and 

 growth, the results must be the same. A single-celled 

 animal with qualities abcxyz divides into two ; each has 

 presumably the qualities of the original unit ; each 

 grows rapidly into the form of the full-grown cell. We 

 have no difncultv in understanding this. In the sexual 



/ C- 7 



reproduction of higher animals, the case is complicated 

 by the formation of the " body," but logically the difficulty 

 is not greater. 



How far has this early separation of the future repro- 

 ductive cells from the developing body been observed ? 

 It has been observed in several worm-types leeches. 

 Sagitta, thread-worms, Polyzoa, in some Arthropods 

 e.g. Moina and Cyclops among crustaceans, in Chironomus 

 and some other Insects, Phalangidse among spiders, and 

 with less distinctness in a number of other organisms, 

 both animal and vegetable. In many organisms, how- 

 ever, the future reproductive cells are not observable till 

 development has proceeded for some time it may be 

 days or weeks longer. Thus we have to pass from cases 

 of a demonstrable lineage of segregated germ- cells to 

 Weismann's more general conception of ' the continuity 

 of the germ-plasm.''' " In each development," he said, 

 " a portion of the specific germ-plasm contained in the 

 parent egg-cell is not used up in the construction of 

 the body of the offspring, but is reserved unchanged 

 for the formation of the germ-cells of the following 

 generation." 



When we remember that a piece of a Begonia leaf, or 



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