FORMATION OF GERMINAL LAYERS IN CBELONIA. 45 



(Taf. iii, Hertwig) of Triton. Our fig. 26 with fig. 4 (Taf. iii) 

 of Triton^ our fig. 27 with fig. 5 (Triton), and, finally, our 

 fig. 28 with fig. 6 (Triton). 



As to the contribution to the raesoblast from the germinal 

 wall, there is of course no equivalent in the holoblastic egg of 

 Amphioxus or Amphibia. It seems to us that phylogenetically 

 this source is not of much significance and is brought about 

 wholly by adaptation. Sarasin^s (No. 15) researches on the 

 Reptilian egg have brought out the fact that new cells are 

 added on from the yolk to the blastoderm by a process very 

 similar to budding. Why could we not suppose that this 

 process goes on until considerably later, and that the addition 

 of cells to the mesoblast from the germinal wall is but the 

 continuation of this process? 



We should like to add another suggestion. In Trionyx the 

 primitive streak is continuous with the lateral edges of the 

 blastopore, enclosing the yolk-plug (see fig. 6). Have we not 

 here a case where a part of the original blastopore lips has 

 met in the median line and formed the primitive streak, while 

 the rest of the edge of the blastopore has retained its original 

 condition ? 



We think we have succeeded in showing that the develop- 

 ment of Reptilia harmonises completely with that of Amphibia. 

 Our observations confirm the conclusions which Hertwig 

 formed in regard to the Reptilian development, basing his 

 judgment on the observations of other workers (No. 6, Theil ii), 

 but we hope we have filled in many details not before noticed. 

 We dissent strongly from Strahl, who in two separate publica- 

 tions (Nos. 11 and 13) oppose Hertwig's views. We think 

 Strahl is singularly unfortunate in the interpretation of his 

 sections. 



We think it hardly necessary to go over other papers on the 

 germinal layers of Reptilia (Strahl, Nos. 7, 8, 9, 10, 11, 12, 13 ; 

 Kupffer, No. 5; Weldon, No. 14; Hoffmann, No. 16), and 

 point out the points of similarity and dissimilarity between 

 those workers and ourselves. The reader must refer to the 

 original papers themselves. 



