82 Cell-Pedigrees 



those pedigrees have lately been frequently emphasized 

 A for the animal kingdom by Weismann and others, and a 

 comparison of both kingdoms with reference to this 

 point does not, therefore, offer any considerable diffi- 

 culties. 



2. The Cellular Pedigrees of the Homoplastids 



In unicellular species the pedigrees of the individuals 

 coincide with the cellular pedigrees. But such is also 

 the case with those organisms of few cells, the cells of 

 which are as yet quite alike and not organized for various 

 functions. The Oscillariae are many-celled threads, but 

 all the cells are alike, every one of them is equally able 

 to propagate the species. Gotte has named such organ- 

 isms homoplastids, as compared with the.heteroplastids, 

 the cells of which are adapted for various functions. 



It is clear that the ancestral trees of cellular descent of 

 the homoplastids are entirely composed of like branches. 

 It depends only upon external circumstances, and the 

 struggle for existence, which of the cells will become new 

 individuals, and which branches of the family tree, there- 

 fore, will continue the descent through the series of gen- 

 erations. 



In the higher plants and animals, on the contrary, 

 only definite branches of the cellular pedigree lead, in the 

 normal course of development, to the cells that begin 

 the next generation, the other branches being already ex- 

 cluded, by their nature, from taking part in the normal 

 propagation of the species. The branches of the tree are 

 here, therefore, not only morphologically different, but 

 also intrinsically unlike in their relation to the pedigree 

 of the species. 



The differentiation of the cellular pedigrees started 



