1888.] 



On the Development of Apteryx. 



483 



the only collector I have yet met with who was willing to give his 

 time not only to collecting the eggs, but to removing and preserving 

 the embryos. I have, unfortunately, never been able to leave Dunedin 

 during the breeding season so as to try and procure the earlier stages, 

 the removal and preservation of which could not be entrusted to a 

 collector. 



My first Stage (A) corresponds roughly with a chick embryo of 

 the fourth day of incubation : the full number of mesoblastic somites 

 — about 44 — has already appeared. Stage B is apparently only a few 

 hours older : Stage C corresponds very nearly with a fifth day chick, 

 except that the limbs are in a less advanced condition. 



Stage D is in about the same state of development as a chick of 

 the 7th day ; it was unfortunately damaged by the collector during 

 removal from the egg, both fore-limbs being destroyed. Avian 

 characters are now definitely assumed, the head being produced into 

 a short beak very like that of a chick at the corresponding period. 

 The hind-limbs are still in the primitive position, i.e., stretched out 

 at right angles to the long axis of the body, but their extremities are 

 dilated into flattened paw-like feet which distinctly show the three 

 principal digits and a small knob-like hallux. 



Stage E is a little later than D, and is chiefly interesting for the 

 condition of the fore-limb, which is terminated by a tridactyle paw with 

 sub-equal digits. In the hind-limb the cnemial flexure has appeared, 

 but not the mesotarsal flexure, so that the combined crus and pes are 

 directed backwards. 



In Stage F the characteristic features of the genus Apteryx are 

 assumed, the beak having undergone a great increase in length and 

 bearing the nostrils at the tip. The fore-limb is now a true wing, 

 the manus being supported mainly by the second digit, but presenting 

 blunt projections on the pre- and post-axial borders of the wrist 

 which indicate respectively the positions of the reduced first and 

 third digits. In the hind-limb the mesotarsal flexure has appeared, 

 and the pes has nearly assumed its adult characters. The feather- 

 papillae appear first in this stage. 



In Stage Gr the feather-papillse have become larger and more widely 

 distributed ; the beak and the hind-limbs have further increased in 

 length, and the wing shows no trace externally of either the first or 

 the third digit. In all the remaining stages the adult form is assumed 

 and the body covered with feathers. 



Contrary to the usual statements as to the pterylosis of the Ratitoe, 

 Apteryx has distinct apteria, which are especially noticeable in the 

 earlier stages.* In Stage F, in which the feather-papilla? first appear, 

 they are arranged in fairly distinct dorsal, humeral, and femoral 



* Pterylse and apteria are figured in the embryo ostrich and referred to in the 

 description of the figures by Miss B. Lindsay, ' Zool. Soc. Proc.,' 1885, PL XL1II. 



