EMBRYOLOGY OF CRYPTOBRANCHUS 77 



The envelope is perfectly transparent when fresh, except that 

 wherever viewed tangentially its inner layers have a misty appear- 

 ance, represented by the shaded zone in fig. 1, and due to a fine 

 lamellar structure sketched in optical section in fig. 2. The misty 

 appearance is caused by the diffusion of light passing through 

 these concentric layers in a direction tangential to their surfaces. 

 The core or axis of the connecting cord has the same misty appear- 

 ance, due to a continuation of the lamellar structure. The various 

 layers or lamellae of the gelatinous envelope are in intimate 

 contact; there is no fluid-filled space between them such as occurs 

 between the capsule and the vitelline membrane. 



The inner layer of the lamellar core of the cord in some cases 

 exhibits a marked twisted or spiral arrangement, like that of the 

 inner portion of the cord connecting the eggs of Ichthyophis as 

 described by the Sarasins ('87-'93). 



The eggs of a given spawning are fairly uniform in size, but there 

 is considerable variation in the size of eggs from different parents. 

 The average dimensions of the living egg and its envelopes, after 

 two days' immersion in water, are as follows: 



Diameter of egg proper 6.2 mm. 



Diameter of egg with envelope 18 mm. 



Diameter of connecting cord 5 mm. 



Distance of one egg from another, measured from center to center 



along the cord, about 30 mm. 



A few egg capsules, particularly among the empty ones, are 

 double, formed by the union of two capsules without a connect- 

 ing cord. In such cases the cavities of the two capsules are usually 

 separated only by a thin gelatinous septum; but all gradations 

 occur between this condition and that in which two capsules are 

 connected by an unusually short cord. Rarely, three capsules 

 are closely approximated. 



I have found a few instances in which two eggs occurred in 

 the cavity of one simple capsule, without any separation by a gela- 

 tinous membrane. It would seem possible that double embryos 

 might be formed in this way, by the fusion of the yolk masses of 

 two such eggs; but this could not account for the only double 



