OUTLINES OF THE DEVBLOPAJENT OF THE TUATARA. 59 



the nerve of the parietal eye makes its appearance in connection 

 with the outer layer. 



A small quantity of pigment also appears on the floor of the 

 hollow distal portion of the '' stalk." 



Stage S. 



To this stage I refer embryos numbered 138, 139, and 140, 

 which reached me on January 6th, 1898, having unfortunately 

 died on the voyage, still enclosed in the shell ; and 149 and 150, 

 which are the " skeletons " referred to by Mr. Henaghan ^ as 

 having been found dead on Stephens Island about the middle 

 of January. All these embryos were evidently very nearly ready 

 to hatch when they died ; in fact, in the case of Nos. 149 

 and 150 the shell was already ruptured and the embryo par- 

 tially extricated. The following description is based upon 

 Nos. 138, 139, and 140, which seem to be a little less 

 advanced. 



The animal now closely resembles the adult, except in point 

 of size. The total length from the tip of the snout to the tip 

 of the tail in the specimen measured was 92 mm.; from the 

 cloacal aperture to the tip of the tail 50 mm. ; length of head 

 from the tip of the snout to the level of the jaw-angles 15 mm. ; 

 width of head between the angles of the jaw 12 mm. 



A yolk-sac about 12 mm. in diameter, densely packed with 

 yolk, is still attached to the embryo by a narrow stalk a short 

 way in front of the cloacal aperture, which now forms a large 

 transverse slit. 



Scales and claws are present as in the adult. The nuchal 

 and caudal crests of spines are also present, the former as yet 

 very small, the latter well developed; while the dorsal crest is 

 not yet recognisable. 



The ''shell-breaker^^ is still present, but relatively small as 

 compared with the preceding stage. It appears to be repre- 

 sented in the adult by the especially large scale at the apex of 

 the snout. 



The palatine, maxillary, and posterior mandibular teeth are 

 'Vide Introduction. 



