MISCELLANEOUS NOTES. 205 



No. XXII— REMARKS ON THE EMBRYOLOGY OF A SNAKE. 



It has been my good fortune this year to acquire snake's eggs with the 

 embryo in a very early stage of development. Doubtless the ontogeny of 

 ophidiaus has been worked out before by men of much greater ability than 

 myself. I have, however, never seen any account of the development of the 

 snake, and have tried unsuccessfully for some years to see the embryos in a 

 very early stage. I hoped, if I could get them early enough, to be able to 

 throw some light on the phylogeny, through studying the ontogeny. 



The youngest embryos I extracted from eggs believed to belong to Tropido- 

 notus stolatus and when unravelled measured only 1^" in length. The hatch- 

 lings of this snake I know to be from 5%" to 6|" inches long, so the length of 

 these embryos show they are in a very early stage of development, still they are 

 not young enough yet to satisfy me. The following points arrested my atten- 

 tion. The head posteriorly has a large swelling (the primary cerebral vesicle) 

 denoting the early development of the brain. This is, at this stage, a single 

 rounded eminence. Later it is divided by a median sulcus into two (fig. H). 

 The eye is large, and the pupil discernible. The upper jaw is fully developed, 

 but the lower, which is developed like the upper from the first gill arch, is in a 

 very rudimentary state (see fig. F 2). The mouth is very large. No trace of 

 an external ear orifice can be discerned. Only one gill arch is present, and 

 there are no branchial clefts or fringes. The heart is large, and could be seen 

 pulsating for a long time (half an hour) after removal of the embryo from 

 the egg. The two auricles and the single ventricle are very apparent, I was 

 much disappointed to find no trace of either fore or hiud limbs. 



Figures G, H and I are from a larger embiyo measuring 3 inches. Here 

 the lower jaw is properly developed. The pupil and iris are distinct, and the 

 primary cerebral vesicle is relatively smaller, and has become divided mesially. 

 The genitals in the males are relatively long, and are quite external. At what 

 date they become ensheathed I have not yet been able to discover, but it is 

 late during life within the egg. 



Figures A to F shows successive stages in development. 



A. The foetus in membranes. 



B. The foetus still in membranes the head freed. 



C. Membranes peeled off. still partially adherent (a). 



D. In profile showing spiral form of body. 



E. Head seen three-quarter view with large cerebral vesicle on top. 



F. Foetus unravelled. 1. The primary cerebral vesicle. 2. Rudimentary 

 lower jaw. 3, 4, 5, Heart. 



