224 The Unity of the Organism 



resembles the larva of encliinodernis so much that its dis- 

 coverer believed it to belong to this group and for a long 

 time zoologists accepted this view, the truth about it com- 

 ing out only when the transformation of tlie larva into the 

 adult was actually observed. For non-zoological readers 

 it may be stated that Balanoglossus is a worm-like creature 

 about as unlike a sea-urchin or a starfish as can be im- 

 agined. The truth is, it is only by ohservational connpara- 

 tive studies that embryologists are able to predict at all 

 either the earlier or the later unobserved stages, pertaining 

 to the developmental career of an animal. 



If speculation on the nature of germ-cells had followed 

 consistently these familiar and universal principles, the 

 literature of biology would be unburdened to-day of a vast 

 load of useless writings. Let any biologist ordinarily prac- 

 ticed in the methods of embryology ask himself candidly 

 what he would expect to find in the living fertilized Qgg of a 

 starfish, for instance, were some manufacturer of micro- 

 scopes to furnish him with an instrument that would mag- 

 nify with good definition to a million diameters. Can he 

 consistently suppose he would see something "carrying" all 

 the innumerable characters of the adult starfish? Why has 

 he any more right to suppose he would recognize the char- 

 acters of the adult in the germ-cell than that he can recog- 

 nize them in the larva just before metamorphosis, or in any 

 other stage .^ Yet what embryologist has ever talked about 

 the characters of the adult starfish being "carried" by ele- 

 ments of the larva? What we are justified in believing on 

 the basis of the inductive evidence in our possession is that 

 such a microscope would enable us to recognize many struc- 

 tural features peculiar to the particular species of starfish 

 at that particular stage of the individual's life, and that as 

 development proceeded these egg-stage features or char- 

 acters would disappear and other characters distinctive 

 of the embryonal stage, the larval stage, and so on, would 



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