OUTLINES OF THE DEVELOPMENT OF THE TUATAEA. 53 



The allantois {All.) is also in an abnormal condition, being 

 collapsed and shrivelled. 



In the body of the embryo itself little advance is visible, at 

 any rate as regards external characters ; and, having only a 

 single specimen in a doubtful state of preservation, I have not 

 cut any sections. In the paired eyes the choroidal fissure is 

 still just recognisable. No pigment is yet visible externally in 

 the parietal eye. The fronto-nasal process is still widely sepa- 

 rated from the superior maxillary processes, but has developed 

 a small median projection which becomes much more prominent 

 at the next stage. The external opening of the hyomandibular 

 cleft {H. M. C.) has become very small, but is still plainly 

 visible. No trace of digits is yet present externally in manus 

 or pes. 



In shortj the only important difference between this stage 

 and the preceding lies in the complete extrication of the 

 embryo from the yolk-sac, and the accompanying elongation of 

 the splanchnic stalk. 



Stage Q (figs. 103, 103). 



This stage is again represented by only a single embryo, 

 No. 1, collected on Stephens Island on January 18th, 1897. 

 Unfortunately the eggs sent in this first consignment all dried 

 up in transit, the sand in which they were packed not having 

 been sufficiently moist, and the embryo represented in figs. 101 

 and 102 was the only one of any service. This embryo was 

 dead when received, but still in a sufficiently good state of 

 preservation as regards external characters. 



It exhibits a marked advance upon the preceding stage in the 

 following features : 



(1) The fronto-nasal and superior maxillary processes have 

 united so as to complete the upper margin of the mouth, in the 

 middle of which a prominent beak-like projection is visible 

 (fig. 103). 



(2) In consequence of this the external nares (fig. 103, Na.) 

 have become delimited as a pair of small crescentic apertures. 



