XIV. ON THE EARLY DEVELOPMENT OF THE LACERTILIA, 

 TOGETHER WITH SOME OBSERVATIONS ON THE NATURE 

 AND RELATIONS OF THE PRIMITIVE STREAK*. 



(With Plate 29.) 



TILL quite recently no observations were recorded on the 

 early developmental changes of the reptilian ovum. Not long 

 ago Professors Kupffer and Benecke published a preliminary 

 note on the early development of Lacerta agilis and Emys 

 Europea?. I have myself also been able to make some observa- 

 tions on the embryo of Lacerta mnralis. The number of my 

 embryos has been, somewhat limited, and most of those which I 

 have had have been preserved in bichromate of potash, which 

 has turned out a far from satisfactory hardening reagent In 

 spite of these difficulties I have been led on some points to very 

 different results from those of the German investigators, and to 

 results which are more in accordance with what we know of 

 other Sauropsidan types. I commence with a short account of 

 the results of Kupffer and Benecke. 



Segmentation takes place exactly as in birds, and the result- 

 ing blastoderm, which is thickened at its edge, spreads rapidly 

 over the yolk. Shortly before the yolk is half enclosed a small 

 embryonic shield (area pellucida) makes its appearance in the 

 centre of the blastoderm, which has, in the meantime, become 

 divided into two layers. The upper of these is the epiblast, and 

 the lower the hypoblast. The embryonic shield is mainly dis- 

 tinguished from the remainder of the blastoderm by the more 

 columnar character of its constituent epiblast cells. It is some- 

 what pyriform in shape, the narrower end corresponding with 



1 From the Quarterly Journal of Microscopical Science, Vol. xix. 1879. 

 z Die Erste Enlwickluiigsvorgd/igc am Eider Rcplilien, Konigsberg, 1878. 



