SUMNER: KUPFFER'S VESICLE 71 



KOPSCH concludes from these results that, at the time of the first appearance of 

 the embryonic Anlage, the head rudiment (K, figure 31, A) is median, the cell- 

 masses (R) destined for the halves of the trunk and the tail are laterad to this. The 

 formation of the caudal knob ("Knopf," R, figure 31, B) results from the union 

 of the two lateral masses behind the head rudiment. The " Knopf" is the re- 

 pository for the trunk and tail Anlagen, which thus, even at this early stage, 

 come to lie in the middle line. The caudal knob does not, however, depend for its 

 growth entirely upon a multiplication of its own cells but, during the circumcres" 

 cence of the germ-ring, receives successive portions of the latter, which serves merely 

 as so much undifferentiated building material. A concrescence in the sense em- 

 ployed by His, he says, does not occur in the Salmonidne. The process by which the 

 two rudiments (R) came together KOPSCH does not consider as concrescence, although 

 he does not give sufficient reason for his position. He makes the very significant 



FIGURE 31. 



Diagrams illustrating Kopsch's view of the formation of the embryo from the germ-riug. K, head anlage. 



R, material destined to form the trunk. 



remark that the Knopf " contains the neurenteric canal," although not stating just 

 what he means by this. In a later paper ('99), he says that the Knopf is " com- 

 posed of two symmetrical halves which are separated from one another by the ideal 

 neurenteric canal." 



The above conclusions of MORGAN and KOPSCH are in no way inconsistent with 

 the results of HENNEGUY'S measurements. HENNEGUY located the growing region 

 of the embryo between Kupffer's Vesicle and the most recently formed somite. 

 This HENNEGUY offered as convincing evidence against concrescence by apposition, 

 and in doing this he seems to have struck the first decisive blow against His's the- 

 ory. If concrescence (confluence) is occurring at all, he says, it occurs in front of 

 Kupffer's Vesicle. This supposition, however, he also rejects for reasons which I 

 shall not here discuss. It will be remembered that HENNEGUY believed the caudal 

 knob (and this only) to be formed through an actual process of concrescence proper. 



