6 K. MITSUKURI; 



( 92, p. 34) : — " Wir sehen dass nur der vordere Abschnitt* sich an 

 der Bildung der Einstülpung betheiligt, während der hintere* sich 

 lediglich auf die Zellen Wucherung beschränkt, im Niveau der 

 Keimscheibe liegen bleibt resp. über das Niveau der- 

 selben vorragt und das Homologon des Dotterpfropfes 

 der Amphibiengastrula darstellt, der bei den Amnioten 

 passender als Entodermpfropf bezeichnet werden dürfte. 



AVhile all the authors above referred to hold views which are 

 more or less like ours, there are others who have flatly opposed our 

 interpretation. 



IvOBiNSOX and Asshetox ('91) referring to our views as set 

 forth in Contribution I. of the present series says : — * * * and 

 in the tortoise, according to Mitsukuei and Ishikawa, the primitive 

 streak consists, in the first instance, mainly of a mass of hypoblast or 

 yolk, which they compare to the yolk-plug of Amphibians. To this, 

 however, it cannot correspond, for we have already shown that the 

 yolk-plug of Rana is a portion of the ventral wall of tiie archenteron, 

 whilst the primitive streak is formed by the fusion of the lateral lips 

 of a deficiency in the posterior wall of the same cavity. "f (p. 477). 



* I.e., of the prioiitive plate. For the definition of this term, see further on. 



t The above quotation shows that Robinson and Assheton have somewhat misunderstood 

 our position, for we have never represented the mass in question to be a part of the primitive streak. 

 That name we assigned, in our Contrih. I., to a short axial strip, situated directly behind the yolk- 

 plug where the epiblast is proliferating cells to the mesoblast {Fig. 8, Contrih. I.). This we re- 

 garded as caused by the coalescence of the posterior part of the blastopore lips, and not marked 

 off from the yolk-plug, as it should Ije, because the posterior boundary of the yolk-plug remains 

 rudimentary [See Firj. G, Contrih. I.). This misunderstanding does not, however, affect the fact 

 that Robinson and Assheton are opposed to our views on the yolk-jjlug homology. In a 

 private letter to me, Dr. Robinson says : " * * * at present I am convinced that the mass of 

 cells in the tortoise which you have figured and called the yolk-plug is a part of the primitive 

 streak and is therefore not cooiparable with the yolk-plug of Ami3hibians * * ." In jDassing 

 I may remark that what we called the primitive streak in our Contrih. I., as explnined above is 

 the hindermost part of the primitive streak, if it is a part at all. The name, primitive streak 

 should be given to an entirely different formation, as the facts brought out in the present 

 Contriljution will show. 



