146 The Unity of the Organism 



stages, do occur. To make the case quite satisfactory fail- 

 ure to fuse ought to be shown between species both of which 

 are able, and about equally able, to develop into typical 

 animals of their own species. 



But the evidence of specificity of the protoplasm of the 

 different species indicated by the experiments is by no means 

 restricted to the nonfusibility of the cells of the several ani- 

 mals. Quite as conclusive is difference in behavior of the 

 various preparations. Although Wilson does not go into 

 this particularly, his experiences show that the tissues of 

 Microciona produce young sponges considerably more read- 

 ily than do those of the other species when treated in exactly 

 the same manner. As to the relative viability and develop- 

 ability of dissociated cells of Lissodendoryx and Stylotella 

 the descriptions are not full enough to enable one to decide. 

 A comparison of the species on the basis of quantitative 

 determinations of both the extent of development and the 

 conditions of the water under which the development takes 

 place would probably settle this and would be highly in- 

 structive. 



Another investigator, Karl Miiller, reports that the dis- 

 sociated cells of individuals of different species are able to 

 fuse together but that the fusion masses "never regenerate 

 to small sponges." No details are given under this head, 

 but are promised in a later publication. 



Obviously the fusibility or non-fusibility of isolated tis- 

 sues as brought out by experiments of this kind are phe- 

 nomena close of kin with those of the degree of compati- 

 bility of grafts in the ordinary sense with the "stock" upon 

 which they are grafted. It was mentioned in another con- 

 nection that we now have sufficient information about graft- 

 ing in animals to show that much the same rules hold here 

 as among plants. 



Morgan reviews the work that has been done in animal 

 grafting, and sums up the results on the congeniality be- 



