594 ON THE EARLY STAGES IN THE DEVELOPMENT OF THE EMU, 



The only later stage examined was an embryo of seven days,, 

 which had attained to about the same grade of development as a 

 60 hours' chick, with well developed vascular area, heart bent 

 upon itself, viscei-al arches and clefts, cranial flexure well marked, 

 lens-involution still connected with the epiblast, auditory sac still 

 opening on the exterior, and with the amnion completel}' covering 

 the whole surface with the exception of a small key-hole-shaped 

 aperture above the posterior end of the medullary canal. 



Tn this specimen (plate XV, figs. 24-28) there is in the caudal 

 region, just behind the posterior end of the notochord a passage 

 (neurenteric canal) from the hinder end of the medullary canal to 

 the hind gut. This corresponds in position to the neurenteric 

 canal already described at a much earlier stage ; but whether it is 

 the same canal or a fresh formation is uncertain. It is the equivalent 

 seemingly of a canal which has sometimes been observed in the 

 fowl in the middle of the third day of incubation.* 



LITER ATURE.t 



I. — Balfour, F. M. A Treatise on Comparative Embryology. 



II.— Balfour, F. M., and Foster, M. Elements of Embryology. 



III.^Balfour, F. M., and F. Deightok. A renewed Study of the 

 Germinal Layers of the Chick. Quart. Journ. Micro. Sci. 

 XXIL, 1SS2, and Studies from the Morph. Lab. of Cambridge 

 University ; and Works, Memorial P^dition, Vol. I., p. 854. 



IV. — Balfour, F. M. The Development and Growth of the Layers 

 of the Blastoderm. Q. J. Micro. Sci. XIL, 1873 ; and Works, 

 Memorial Edition, Vol. I., p. 29. 



* Rauber, XXIX. p. 147. 



t This is not intended as a complete biblioarraphy, including as it does only such works 

 and papers bearing on the subject as 1 have been able to consult. In a good many instances 

 in whicli the publications are not represented in Sydney Libraries, I have gained a general 

 knowledge of their contents from the abstracts in the ' Zoologischer Jahresbericht,' and as I 

 have had to refer to these, I ha\e entered them, adding the number of the voliune of the 

 ' Jahresbericht ' in parenthesis. 



