FORMATION AND FATE OF THE PRIMITIVE STREAK. 121 



intervals small evaginations from the archenteron (fig. 6, D), but these 

 small diverticula cannot be traced for any great distance into the 

 mesoblastic plates. 



They remain for a time as blind diverticula, and then they disappear. 

 So far as we have been able to discover they do not communicate with 

 the coelom, and the coelom is not formed by extension of the archenteric 

 diverticula, as in Amphioxus, but by a splitting of the mesoblast which 

 first occurs laterally, and then extends dorsally and ventrally as in 

 the higher Vertebrata. 



Alphabetical List of Literature referred to. 



1. Balfour, F. M. — ' Comparative Embryology,' vol. ii, London, 1881. 



2. Balfour, F. M., and Deighton, F. — "A. Renewed Study of the Germinal 



Layers of the Chick," 'Quart. Journ. Micr. Sci.,' N. S., vol. xxii, 

 pp. 176—188. 



3. Van Beneden, E. — "TJntersuchungen uber die Blatterbildung des 



Chordakanals und die G-astrulation bei den Saugetieren, Eaninchen und 

 Vespertilio murinus betreffend," ' Anatomischer Anzeiger,' Jahr. iii, 

 pp. 709—714. 



4. " Developpement embryonaire des Mammiferes," 'Bulletin de l'Acadeniie 



Belgique,' 1875. 



5. Bonnet, E. — f< Beitrage zur Embi'yologie der Weiderkauer, gewonnen 



am Schafei," 'Archiv fiir Anatomie und Physiologie — Anatomische 

 Abtheilung,' 1884, pp. 170—230, plates ix— xi. 



6. Ibid, 1889, pp. 1—106, plates i— vi. 



7. " Ueber die Entwickelung der Allantois und die Bildung des Afters bei 



den Wiederkauern und uber die Bedeutung der Primitivrinne und des 

 Primitivstreifs bei den Embryonen der Saugetiere," ' Anatomischer 

 Anzeiger,' Jahrg. iii, 1888, pp. 105—126. 



8. Calberla, E. — " Zur Entwickelung der Medullarrohres und der Chorda 



dorsalis der Teleostier und der Petromyzonten," pp. 226 — 270, plates 

 xii and xii, ' Morphologisches Jahrbuch,' 1877. 



9. Durham,. — Notes on the Presence of a Neurenteric Canal in Rana." 

 ' Quart. Journ. Micr. Sci.,' N. S., 1886, pp. 509, 510, plate xxvii. 



10. Duval, M. — " De la formation du blastodern dans l'ceuf d'oiseau," 



'Annales des Sciences Naturelles — Zoologie,' vol. xviii, 188i, pp. 1 — 208. 



10a, Erlanger, R. — "Ueber den Blastoporus der anuren Amphibien, sein 

 Schicksal und seine Beziehungen zum bleibenden After," ' Zoologische 

 Jahrbucher,' 1890, pp. 239 — 256, plates xv and xvi. 



11. Fleischmann, A. — " Embryologische Untersuchungen — Erstes Heft," 



' Einheimische Raubtiere,' Wiesbaden, 1889. 



