70 MEMOIRS OF THE NEW YORK ACADEMY OF SCIENCES 



Vesicle, there would be a rapid increase in the distance between the latter and the 

 caudal end. But this, as HENNEGUY was first to point out is untrue. The writer 

 has verified HENNEGUY'S observations, which were made upon trout embryos, by 

 camera lucida measurements made upon the living egg of Scorpsena. Whether, 

 however, there occurs, after the appearance of the caudal knob, a process of con- 

 crescence in the second sense ("confluence") is a question upon which my own 

 observations throw little light. [See Supplement.] The experiments of other in- 

 vestigators, as we shall see, speak strongly for this view. 



Experiments of Morgan and Kopsch. MORGAN ('95), l working upon the egg 

 of Fundidus, performed the crucial experiment of cutting the germ-ring to one side 

 of the embryo. In a number of cases, nearly normal embryos developed in spite of 

 their severance from the hypothetical sources of building material. He rejects, on 

 what seems to me to be insufficient grounds, the supposition that a process of regen- 

 eration has taken place on the injured side. MORGAN'S accounts, it is important to 

 note, mentions two cases in which injury to the germ-ring resulted in a deficiency of 

 mesoblast on tbe corresponding side of the embryo. For this and other reasons he 

 concludes that the germ-ring normally does, in part at least, pass into the embryo 

 during growth, but he also holds that it furnishes a relatively small part of the sub- 

 stance of the latter. 



The experiments conducted by KOPSCH ('96) 2 upon the egg of the trout differ 

 from those of his predecessor mainly in being more systematic and thorough. He 

 finds that the effects of injuring the germ-ring vary with the position of the injury 

 and the stage at which it is inflicted. After the caudal knob has appeared, any in- 

 jury to the germ-ring laterad to this does not prevent the corresponding side of the 

 embryo from developing with a normal number of somites. This side is, however, 

 less strongly developed, in point of quantity of mesoblast, than the opposite (thus 

 agreeing with MORGAN). Injury to the embryo during an early " embryonic shield" 

 stage, before a tail-bud has appeared, gives results varying according to the location 

 of the injury. If the latter is in the center, no growth takes place here, but the 

 "non-embryonic" borders of the blastoderm continue to surround the yolk, leaving 

 the punctured spot, at the time of closure, at the (anterior) end of a long slit. If 

 the injury is slightly laterad, an embryo develops, having a perfect head, but the 

 trunk fails to develop on the injured side. If the injury is still further laterad, an 

 embryo results but not so strongly developed on the injured side (see above). 



1 A preliminary account of these experiments is to be found in the Aunt. Anz., 1893. KASTSCHKNKO, in 1888, 

 had performed similar experiments upon the Selachian embryo, his results leading him to oppose the concrescence theory. 



2 KopSCH's later experiments ('99) in producing artificial Hemididymi I shall not discuss, inasmuch as his results 

 are equally well explained upon the orthodox view of concrescence. 



