No. 2.J EMBRYOLOGY OF THE AMERICAN ALLIGATOR. 1 89 



Jungen schliipfen nach ungefahr zwei Monaten, beim Eintritt 

 der grossen Regenzeit aus. Thatsachlich war das Thier bei 

 unserer Annaherung auf dem Nest gewesen. Die Eiablage 

 erfolgt nur einmal im Jahre, in der Zeit von Ende Januar bis 

 Anfang Februar." 



The Egg. 



The eggs are white, elliptical, and vary in length from 50 to 

 90 mm., and in the shorter diameter from 28 to 45 mm. Gen- 

 erally there is only slight variation in the eggs of one nest, but 

 occasionally a nest is found in which most of the eggs are about 

 average size, while from two to five are very much smaller. In 

 one such nestful I found four smaller eggs of different sizes, 

 forming a very perfect series to the smallest, which measured 

 only 28 by 50 mm. It is represented by the innermost outline 

 in PI. IX, Fig. 2. The other lines of the figure represent the 

 outlines of four other eggs from various nests, and illustrate 

 the differences in size. An exterior view of a medium size egg 

 is shown in Fig. 4, and Fig. 3 is a similar view of the egg of 

 the Florida crocodile. The shell is much rougher than that of 

 a hen's egg and much thicker. Upon treatment with hydro- 

 chloric acid there remains a white organic matter which swells, 

 becoming thicker than the original shell. The shell membrane 

 is very thick, much more so than that of the hen's egg, and 

 consists of two layers, — an inner and an outer, — in both of 

 which the fibres are arranged spirally about the egg, but at 

 right angles to one another. In a fresh-laid egg the shell is 

 uniform in appearance throughout, and the same is true of the 

 shell membrane. But there soon appears an area of a chalk- 

 white color on the shell, which, beginning near the middle, 

 extends gradually around the smaller diameter in the form of a 

 median belt or zone. Upon removing the shell the cause of 

 this change is seen to lie in the shell membrane. This has 

 changed in appearance in just that area covered by the chalk- 

 white zone in the shell ; it has become opaque white and looks 

 drier, with a rougher surface, while the remainder of the shell 

 membrane is smooth and translucent : this area increases in 

 width until it finally covers more than half of the egg. Fig. 1, 

 PL IX, shows the outline of this zone on a shell membrane at 

 three different times : the innermost line (1) was the outline 



