The Early DcvGloi)mcnt of the Pigeon's Egg. 53 



are used up, and then there are only the central area and the periblast. 

 The marginal cells constitute a zone of junction between the blasto- 

 disc and the periblast. 



3. The Segmentation Cavity. — The first horizontal cleavage plane 

 marks the position of the segmentation cavity. The blastodisc be- 

 comes stratified by horizontal })lanes arising above this one, and the 

 bird's egg in this respect is homologous with other vertebrate eggs. 



4. The periblast of the bird's egg is the homologue of the 

 cells of the vegetative pole of holoblastic vertebrate eggs. 



LITERATURE. 

 Agassiz, a., and Whitman, C. O., '84. On the Development of some Pelagic 



Fisb Eggs. Preliminary Notice. Proc. Amer. Acad. Arts and Sciences, 



XX. 

 Agassiz, A., and Whitman, C. O., 'St). The Development of Osseus Fishes. 



Memoirs of the Museum of Comparative Zoology at Harvard College. 



XIV, p. 1. 

 Ballowitz, Emil, '03. Die Entwickelungsgeschichte der Kreuzotter (Pelia» 



berus Merr). Tell I. Die Entwickelung vom Auftreten der ersten 



Furche bis zum Schluss des Amnios. Jena. 

 Blount, Mary, '07. The early Development of the Pigeon's Egg with espe- 

 cial reference to the Supernumerary Sperm Nuclei, the Periblast and 



the Germ Wall. A preliminary paper. Biological Bulletin, Vol. XIII, 



No. 5. 

 BoNNEViE, Kristine, '07. Untersuchung iiber Keimzellen Bryozoen. Jena- 



ische Zeitschrift fiir Naturwissenschaft. Vol. XLII, 1907. 

 von Brunn, a., '82. Die Riickbildung uicbt ausgestossener Eierstockeier 



bei den Vogeln. Beitriige zur Anat. u. Embr. als Festgabe. J. Ilenle, 



1882. 

 Duval, '84. De la Formation de Blastoderm dans I'Oeuf d'Oiseau. Ann. 



des Scienc. natur. Zoologie. Series 6. Tome XVIII. 

 Harper, E. H., '04. The Fertilization and early Development of the Pigeon's 



Egg. Amer. Jour, of Anat., Vol. Ill, No. 4. 

 Henning, H., '92. Untersuchung iiber die ersten Entwicklungsvorgange in 



den Eiern der Insekten. III. Zeitschrift fiir wissenschaftliche Zoologie, 

 Bd. LIV. 

 Henneguy. F., "02. Sur la formation de I'oeuf, la maturation et la feconda- 



tion de I'oocyte chez le Distomum hepaticum. Compt. rend. Acad. Sc, 

 Paris. T. 134, p. 123.5. 

 IIis, Wm., '00. Lecithoblast und Angioblast der Wirbelthiere. Abhand- 



lungen der Konigl. SJichs. Gesellschaft der Wissenschaften. 45. Math.- 



Phys., Classe 26. Leipzig. 



