272 
r. M. BALFOUR. 
yolk is much more frequent in the hypoblast than in the epi- 
blast ; and it is well known that a large number of the 
changes in early development are caused by food-yolk. If, 
therefore, the mesoblast has been derived from the hypoblast, 
many more changes might be expected to have been intro- 
duced into its early development than if it had been derived 
from the epiblast. At the same time the hypoblastic origin of 
the mesoblast would assist in explaining how it has come 
about that the development of the nervous system is almost 
always much less modified than that of the mesoblast, and 
that the nervous system is not, as might, on the grounds of 
analogy, have been anticipated, developed in the mesoblast. 
List of Fallen, 
(1) Allen Thomson. British Association Address, 1877. 
(2) A. Agassiz. “Embryology of the Ctenophorse,” ‘Mem. Amer. 
Acad, of Arts and Sciences,’ vol. x, 1874. 
(3) K. E. voN Baer. ‘ Ueb. Entwicklungsgeschichte d. Thiere.’ K6- 
nigsberg, 1828 — 1837. 
(4) E. M. Balfour. “ A Comparison of the Early Stages in the De- 
velopment of Vertebrates,” ‘Quart. Journ. of Micr. Sci.,’ vol.'xv, 1875. 
(5) C. Claus. ‘Die Typeulehre u. E. Haeckel’s sg. Gastraea-theorie.’ 
Wien, 1874. 
(6) C. Claus. ‘ Grundziige d. Zoologie.’ Marburg und Leipzig, 1879. 
(7) C. Gegenbaur. ‘ Grundriss d. vergleichenden Anatomie.’ Leipzig, 
1878. Vide also Translation. ‘Elements of Comparative Anatomy.’ 
Macmillan & Co., 1878. 
(8) A. Gotte. ‘ Entwicklungsgeschichte d. Unke.’ Leipzig, 1874. 
(9) E. Haeckel. ‘Studien z. Gastrsea-theorie,’ Jena, 1877; and 
also ‘ Jenaische Zeitschrift,’ vols. viiiand ix, 1874-5. 
(10) E. Haeckel. ‘ Schopfungsgeschichte,’ Leipzig. Vide also Trans- 
lation. ‘ The History of Creation.’ King & Co., London, 1876. 
(11) E. Haeckel. ‘ Anthropogenie,’ Leipzig. Vide also Translation. 
‘ Anthropogeny.’ Kegan Paul & Co., London, 1878. 
(12) B. Hatschek. “Studien iib. Entwicklungsgeschichte d. Anneli- 
den,” ‘Arbeit a. d. Zool. Instit. d. XJniver. Wien,* von 0. Claus, 1878. 
(15) 0. and R. Hertwig. “Die Actinien,” ‘Jenaische Zeitschrift,* 
vol. xiii and xiv, 1879. 
(14) Th. H. Huxley. ‘The Anatomy of Invertebrated Animals.* 
Churchill, 1877. 
(16) A. Kowalewsky. “ Embryologische Studien an Warmern u. Ar- 
thropoden,*’ ‘Mem. Acad., Petersbourg,’ series vii, vol. xvi, 1871. 
(16) E. R. Lankester. “ On the (terminal Layers of the Embryo as 
the Basis of the Genealogical Classification of Animals,*’ ‘ Ann. and Mag. 
of Nat. Hist.,’ 1873. 
(17) E. R. Lankester. “Notes on Embryology and Classification,” 
‘ Quart. Journ. of Micr. Sci.,’ vol. xvii, 1877. 
(18) E. Metsciiinkoff. “Zur Entwicklungsgeschichte d. Kalk- 
schwamme,” ‘ Zeit. f. Wiss. Zool.,’ vol. xxiv, 1874. 
(19) E. Metsciiinkoff. “ Spongiologische Studien,” ‘ Zeit. f. Wiss. 
Zool.,’ vol. xxxii, 1879. 
