27O J. THOS. PATTERSON. 



halves of the 'dorsal lip of the blastopore. The main evidence 

 in support of this view is derived from experimental data, which 

 will be presented in a future paper. 



It gives me pleasure here to acknowledge my indebtedness to 

 Professor Whitman, under whose direction the work has been 

 carried on, and also to Professor F. R. Lillie for help and criticism. 

 Hull Zoological Laboratory, 

 University of Chicago, 

 July 10, 1907. 



Common Reference Letters used in the Figures. 



A Anterior end of the blastoderm. N Periblastic nuclei. 

 AC Archenteric cavity. O Region of overgrowth. 



B Blastopore. P Posterior end of the blastoderm. 



E Invaginated or gut-entoderm. R Dorsal lip of the blastopore. 



EC Ectoderm. SC Segmentation cavity. 



F Floor of the subgerminal cavity. SG Subgerminal cavity. 

 GW Germ-wall. V Vitelline membrane. 



L Anterior limit of the gut-entoderm. Y Yolk zone. 



M Yolk masses. Z Zone of junction. 



LITERATURE CITED. 



1. Agassiz, L., and Whitman, C. 0. 



'84 On the Development of Some Pelagic Fish Eggs. — Preliminary Notice. 

 Proc. of the Amer. Acad, of Arts and Sci., Vol. XX. 



2. Assheton, R. 



'96 An Experimental Examination into the Growth of the Blastoderm of the 

 Chick. Proc. Roy. Soc. London, Vol. LX. 



3. Blount, Mary. 



'07 The Early Development of the Pigeon's Egg, with especial reference to the 

 Supernumerary Sperm'Nuclei, the Periblast and the Germ-wall. — A Prelimi- 

 nary Paper. Biol. Bull., Vol. XIII. 



4. Duval, M. 



'84 De la Formation du Blastoderme Dans L'ceuf D'oiseau. Annales Des Sci. 

 Nat., 6 Serie, Vol. XVIII. 



5. Gasser, E. 



'82 Beitrage zur Kenntnis der Vogelkeimscheibe. Arch. f. Anat. u. Physiol. 



6. Harper, E. H. 



'04 The Fertilization and Early Development of the Pigeon's Egg. The Amer- 

 ican Journal of Anatomy, Vol. III. 



7. Hertwig, 0.— Mark. 



'99 Text-book of Embryology. 



8. Koller, C. 



'81 Untersuchungen iiber die Blatterbildung im Huhnerei. Arch. f. Mik. Anat., 

 Bd. XX. 



