OUTLINES OF THE r)EVELOP]\[ENT OF THE TUATARA. 43 



characteristic figure-of-8 form of the clear-looking area of the 

 hlastoderni surrouiuling the emhryo. 



In No. 48 the heart was observed to be beating in the living 

 embryo, but very slowly. 



From this stage onwards I propose to describe only those 

 features which seem to be characteristic of each stage, marking 

 a definite advance on the preceding stage, or which otherwise 

 seem to demand special attention, as the organisation has now 

 become so complex that to describe all the remaining stages in 

 full detail would be far beyond the scope of the present paper, 

 especially as the development of the various organs conforms 

 very closely to that of already well-known types. 



Stage K (figs. 74—82). 



To this stage I refer six embryos, as follows : 



38) 



39 > Collected on Stephens Island Nov. 30, removed from egg Dec. 9. 



41 3 



45 „ „ „ 30, „ „ 10. 



49 „ „ „ 30, „ „ IG. 



80 „ „ end of Nov., „ „ 16. 



Embryo No. 39 may be taken as typical of the stage. Tiie 

 general relations of the embryo and foetal membranes re- 

 main as before (vide figs. 74, 75), but the posterior amniotic 

 canal has almost, if not quite, disappeared, having been only 

 doubtfully recognised in a single section. 



The body of the embryo is still straight as far forward as 

 the mid'brain, but the anterior part of the head, including the 

 fore-brain, is bent downwards at more than a right angle, so 

 as to point backwards, thus considerably reducing the interval 

 between the head and the pericardium on the ventral aspect 

 (figs. 74, 75). There is as yet no distinct tail, but the hinder 

 end of the embryo has become, to a certain extent, folded off 

 from the yolk-sac, and projects backwards for a short distance 

 in the pleuro-peritoneal space between the yolk-sac and the 

 serous envelope (fig. 82). 



The alimentary canal has begun to close in behind (figs. 75, 

 82), and the neurenteric canal opens into the short enclosed 



