12 ARTHUR DENDY 



Number 141, size 31 X 23'5 mm. 



„ 142, „ 28 X 21-5 „ 



143, „ 27 X 22-5 „ 



„ 144, „ 33 X 22-5 „ 



Number 145, size 24 X 21 mm. 



146, „ 28 X 21-5 „ 



147, „ 33-5 X 22-5 „ 



148, „ 30-5 X 23 „ 



Eggs containing embryos of otlier stages vary within about 

 the same limits, and it will be seen that their measurements 

 agree closely with those of Thomas (1), who gives the length as 

 varying from 2*5 to 3*35 cm. 



The colour of the eggs is dirty white, stained and mottled with 

 brown by the brown sand or earth in which they are dejjosited. 



The shell is flexible, tough, and elastic, rather rough ex- 

 ternally, and contains in its outer portion a considerable amount 

 of calcareous matter. This calcareous deposit occasionally gives 

 rise to beautiful dendritic or stellate crystallisation patterns 

 on the surface of the egg. The inner surface of the shell is 

 smooth and white, and faintly opalescent. There is no distinct 

 shell membrane, but the shell itself can be readily separated 

 into layers which can be peeled off from one another. 



In the recently laid egg the yellow yolk almost completely 

 fills the shell. Thus the blastoderm wlien formed is separated 

 from the shell by only a very small amount of watery material. 

 Indeed, it is very difficult to open the shell without at the same 

 time piercing the blostoderm and allowing some of the yolk to 

 run out. I have, however, succeeded in puncturing the shell 

 so that only the clear liquid, evidently corresponding to the 

 " white " of a hen's egg, escaped. At a much later stage 

 in the development there is a very large quantity of clear semi- 

 gelatinous material present, which escapes when the egg is 

 opened. This, though closely resembling the " white " of a hen's 

 egg, does not at all correspond to it, but lies inside the allantois, 

 the outer layer of which, being pressed close against the shell, is 

 almost unavoidably punctured with the latter. No air-chamber 

 is present even at a late stage in the development. This fact was 

 specially determined by opening eggs of Stage R under water. 



I have not been able to detect any vitelline membrane ; at 

 the earliest stages observed (c) it appears to have already dis- 

 appeared, or become fused with the blastoderm. 



