464 MORGAN. [Vol. X. 



later stages, producing the appearance of reduction of the material 

 in cross-section, but I have seen no evidence in favor of this view. 

 It is interesting to note that during the later embryonic periods the 

 overgrowth of the germ-ring takes place very rapidly. Sections 

 show that at this time there is very little material present in the 

 germ-ring. It is at this time that we find the embryo elongating as 

 a whole ! 



After the preceding account had been written there appeared a 

 contribution by Locy, in the Anatomischer Anzeiger (No. 13, IX Bd., 

 1894), entitled " Metameric Segmentation in the Medullary Folds 

 and Embryonic Rim " in the Selachian embryo. Locy finds that a 

 superficial beading is present in the germ-ring on each side of the 

 embryo, and he believes that he can trace this into a corresponding 

 beading of the medullary folds. If these headings are not the result 

 of the hardening re-agents they show, as Locy points out, that mate- 

 rial from the germ-ring passes into the embryo. Locy, however, 

 goes further : " The fact that the primitive segments extend into the 

 embryonic rim, and are subsequently drawn into the axial embryo, 

 has an important bearing upon the formation of the latter. It serves 

 to strengthen the view that the germ-ring represents, or originally 

 did, the divided halves of the embryo, and that it is formed in part 

 by their apposition. Thus the doctrine of concrescence receives 

 support from my observations." It may be pointed out that Locy's 

 conclusion does not follow from his premises. If his evidence prove 

 good it shows that some material from the germ-ring goes into the 

 embryo— nothing more. This, however, is also the conclusion that 

 I have now reached in regard to the Teleost. 



Locy says that the evidence from my experiment of cutting the 

 germ-ring only goes to show that the embryo can form without the 

 material from the germ-ring. He says the "experiments undoubt- 

 edly show that it is possible for the constructive material to be 

 brought into the median plane, and for the embryo to elongate when 

 entirely cut off from the germ-ring." I had considered this possi- 

 bility before writing my preliminary account. An attempt to meet 

 this objection will be found in the body of the present paper. 



December 31, 1894. 



