

Further Examination of the Cell-Theory 



consider those animals in which the. egg does not observably 

 foreshadow the adult by any such axial or other differen- 

 tiations as do those we have just been considering. Eggs 

 of this sort, of which those of the sea-urchin and ampliioxus 

 are examples, are preeminently the ones called totipotcnt 

 by Dricsch. Reference to what was set forth in our dis- 

 cussion of totipotence will bring before the reader the fact 

 that eggs of this kind look to be quite devoid of organiza- 

 tion forecastive of the adult stage, but yet are so profoundly 

 stamped in some way with the nature of the species that 

 not only the undivided egg-cell may develop into an adult 

 animal, but each of the first two or four or in some cases 

 even eight blastomeres, may develop into complete animals 

 if the blastomeres be entirely separated from one another. 

 All analogy of observable structure and development war- 

 rants us in believing two things as to the promorphology of 

 these eggs ; first, that there is some sort of organization 

 characteristic of the species to which the particular animal 

 belongs beyond the limits of our present knowledge, and 

 second, that we have little or no means of predicting what 

 that organization is. This second point is of much im- 

 portance from its involvement of embryologies! specula- 

 tions on the nature of the germ. The fundamental fact 

 lost sight of in almost all these speculations is that the 

 transformations and metamorphoses characteristic of all 

 organic development are in their verv essence 1 unforeseeable. 

 The history of biology, and especially of comparative em- 

 bryology, is absolutely conclusive on this point. Over and 

 over again has it happened that certain developmental 

 stages in the life cycle of animals have been discovered be- 

 fore the complete series of stages were known, and that these 

 stages were so different from the adult stages that the pre- 

 dictions made as to the species to which the stages belonged 

 were entirely wrong. The larva of Ilalanoglossus is a fa- 

 mous instance of this in the history of zoology. This larva 



