454 THE MULTIPLICATION OF EFFECTS. 



numerous ones: an J so on continually: eaeh organ as it is de- 

 veloped, serving, by its actions and reactions on the rest, to 

 initiate new complexities. The first pulsations of the foetal 

 heart must simultaneously aid the unfolding of every part. 

 The growth of eaeh tissue, by taking from the blood special 

 proportions of elements, must modify the constitution of the 

 blood: and so must modify the nutrition of all the other 

 tissues. The distributive actions, implying as they do a cer- 

 tain waste, necessitate an addition to the blood of effete 

 matters, which must influence the rest of the system, and 

 perhaps, as some think, initiate the formation of excretory, 

 organs. The nervous connections established among the 

 viscera must further multiply their mutual influences. And 

 so with every modification of structure — every additional 

 part and every alteration in the ratios of parts. Still 



stronger becomes the proof when we call to mind the fact, 

 that the same germ may be evolved into different form- ac^ 

 cording to circumstances. Thus, during its earlier stages, 

 every embryo is sexless — becomes either male or female as 

 the balance of forces acting on it determines. Again, it is 

 well-known that the larva of a working-bee will develop 

 into a queen-bee, if, before a certain period, its food be 

 changed to that en which the larvae of queen-bees are fed. 

 Even more remarkable is the case of certain entozoa. The 

 ovum of a tape-worm, getting into the intestine of one ani- 

 mal, unfolds into the form of its parent : but if carried into 

 other parts of the system, or into the intestine of some 

 unlike animal, it becomes one of the saedike creatures, 

 called by naturalists Ch/sticerei, or Ccenuri, or Echinoc 

 — creatures so extremely different from the tape-worm 

 in aspect and structure, that only after careful investiga- 

 tions have they been proved to have the same origin. 

 All which instances imply that each advance in embryonic 

 complication results from the action of incident f< >rces on the 

 complication previously existing. Indeed, the now 



accepted doctrine of epigenesis necessitates the conclusion 





