124 ARTHUR ROBINSON, M.D., AND RICHARD ASSHETON, M.A. 



47. Schwakz, D. — " TJntersuchungen der Schwanzendes bei den Embryonen 



dei' Wirbelthiere," ' Zeitschrift f iir wissenschaf tliche Zoologie,' xlviii, 

 1889, pp. 191—223, plates xii— xiv. 



48. Scott, W. B., and Osborn, H. F. — " On some Points in the Early 



Development of the Common Newt," 'Quart. Journ. Micr. Sci.,' N. S., 

 1879, pp. 449 — 472, plates xx and xxi. 



49. Sedgwick, A. — "On the Origin of Metameric Segmentation, and some 



other Morphological Questions," ' Quart. Journ. Micr. Sci.,' N. S., 1884, 

 pp. 24 — 42, plates ii and iii. 



50. Selenka, E. — ' Studien iiber Entwickelungsgeschichte der Thiere. — Das 



Opossum/ Wiesbaden, 1886. 



51. Sidebotham, H. — " Notes on the Fate of the Blastopore in Rana 



temporaria," ' Quart. Journ. Micr. Sci.,' N. S., 1888, pp. 49 — 54, plate v. 



52. Spencer, W. B. — " Some Notes on the Early Development of Rana tempo- 



raria"; ' Quart. Journ. Micr. Sci.,' N. S., Supplement, 1885, pp. 123—137, 

 plate x. 



53. Strahe, H. — " Beitrage zur Entwickelung der Keptilien," ' Archiv far 



Anatomie und Physiologie — Anatomische Abtheilnng,' 1883, pp. I — 43, 

 plate i. 



54. " Beitrage zur Entwickelung von Lacerta agilis," ' Archiv fur Anatomie und 



Physiologie — Anatomische Abtheilung,' 1882, pp. 242 — 278, plates xiv 

 and xv. 



55. " Zur Bildung der Cloake des Kaninch en-embryo," ' Archiv f iir Anatomie 



und Physiologie — Anat. Abtheil.,' 1886, pp. 156 — 168, plate iv. 



56. Weldon, B. — " Notes on the Early Development of Lacerta muralis." 



'Quart. Journ. Micr. Sci.,' N. S., xxiii, 1883, pp. 134 — 150, plates iv — vi. 



57. Wenckebach, K. F. — "Der Gastrulationsproce3S bei Lacerta agilis," 



' Anatomischer Anzeiger,' 1891, pp. 57—66 and 72 — 77. 



EXPLANATION OF PLATES III & IV. 



Illustrating Dr. Arthur Robinson's and Mr. Richard Assheton's paper 

 on "The Formation and Fate of the Primitive Streak, with 

 Observations on the Archenteron and Germinal Layers of 

 liana temporaria. '' 



Alphabetical List of Reference Letters for all the Figures. 



A, Anus. a. Anterior extremity of archenteron. A P. Post-anal gut. A R. 

 Archenteron. A R'. That portion of the archenteron the posterior wall of 

 which is formed by the closure of the blastopore. B, B'. Rim of blastopore 



