244 CHARLES R. STOCKARD 



There is also probably some overlapping between the critical 

 moments of origin for the ectodermic organs, for example, those 

 of the central nervous system and the entodermic organs of the 

 alimentary canal. There is, further, the possibility that the 

 interaction or inhibiting influence existing among the buds of 

 one system may not extend to the organ buds of a different sys- 

 tem. I believe, however, that this is not the case, and it is more 

 probable that the growth of each organ affects to a degree the 

 growth of all other parts in the entire embryo. The degrees of 

 effect exerted by one growing organ over the others may differ, 

 for example, the growth of the optic vesicles very probably affects 

 the primary brain ventricle growth more strongly than it does the 

 growth of the branchial organs, etc. 



5. Modifications in size and structural outline of the inner ear: 

 Arrests during a closely similar stage to that in case 4 sometimes 

 show their effectiveness on a different bud. In such cases the 

 ear as well as the mouth and gills becomes affected. The otic 

 vesicle may be completely suppressed or develop into a simple 

 tiny cyst with no outgrowth for the semicircular canals. 



6. Faulty development of the liver and pancreas : Later arrests, 

 after the embryonic line is distinctly seen, in the Fundulus em- 

 bryo may cause an abnormally small outgrowth representing the 

 liver. Such conditions make it appear as though the primary 

 liver bud had been inhibited in its outgrowth from the intestinal 

 wall or the later rate of multiplication of liver cells had been 

 reduced. The pancreas evidently arises and has its critical mo- 

 ment at a somewhat later instant than does the liver. Yet the 

 two moments are so close together that it would require a very 

 deHcate difference in time of arrest to affect the one and not the 

 other. 



The findings in these six attacks on the problem make evident 

 this very important fact: That each organ arises at a definite 

 moment during embryonic development and not during widely 

 different moments just as truly as that an individual organ arises 

 from a very definite embryonic area or anlagen and from no other. 



The organ defects found in nature further confirm the results of 

 experiments on the Fundulus embryos. It is well known from 



