448 ARTHUR ROBINSON. 
formation commences in the region of the primitive streak by 
proliferation of the peristomal cells, and from this region the 
middle layer is extended by proliferation of the greater part of 
the embryonic and a portion of the extra-embryonic hypoblast ; 
but the mesoblast extends into the embryonic area chiefly from 
behind and from the sides, the portion last formed being that 
which enters into the constitution of the protovertebral 
somites. 
List oF LITERATURE REFERRED TO. 
1. F. M. Batrour.—‘ Comparative Embryology,’ London, 1881. 
2. E. van Benepren.—“ Recherches sur lembryologie des Mammiféres. 
La formation des feuillets chez le lapin,” ‘Archives de Biologie,’ 
tome i, 1880, pp. 187—224, plates iv—vi. 
2a. E. van BenepEn.—In the discussion upon Prof. Rabl’s communication, 
Ueber die Bildung des Mesoderms,” ‘ Avatomischer Anzeiger,’ 1889, 
pp. 675, 676. 
23. BE. van Benepven.— Untersuchungen iiber die Blatterbildung, den 
Chordakanal, und die Gastrulation bei den Saugethieren, Kannichen 
und Vespertilio murinus betreffend,” ‘ Anatomischer Anzeiger,’ 
1889, pp. 709—714. 
3. E. van Benepen anp C. Juziy.—‘‘ Recherches sur la formation des 
annexes fcetales chez les Mammiféres,” ‘Archives de Biologie,’ tome 
v, 1884, pp. 371—434, plates xx—xxiv. 
4. BE. van BENEDEN anv C. Jutin.—“ Observations sur la maturation, la 
fécondation, et la segmentation de l’ceuf chez les Cheiroptéres,” 
‘Archives de Biologie,’ tome i, 1880, pp. 553—571, plates xxii, xxiu, 
5. R. Bonnet.—“ Beitrage zur Embryologie der Wiederkauer gewonnen am 
Schafel,” ‘ Archiv fir Anatomie und Physiologie, Anatomische Abtheil- 
ung,’ 1884, pp. 170—230, Taf. ix—xi. 
6. R. Bonnet.—“ Beitrage zur Embryologie der Wiederkauer,” ‘ Archiv 
fiir Anatomie und Physiologie, Anatomische Abtheilung,’ 1889, pp. 
1—106, Taf. i—iv. 
7. G. Broox.—“ The Formation of- the Germinal Layers in Teleostei,” 
‘Transactions of the Royal Society of Edinburgh,’ vol. xxxiii, part 1, 
pp. 199—240, plates xili—xv. 
8. J. T. Cunnincuam.—“ On the Relation of the Yolk to the Gastrula in 
Teleosteans and in other Vertebrate Types,” ‘Quart. Journ, Micr, 
Sci.’ N. S., 1886, pp. 1—38, plates i—iv. 
