6 JOURNAL OF SCIENCE. 



I propose to give a brief account of the salient points in the 

 development of the Kiwi, pointing out their bearing upon the three 

 theories just enuntiated. 



In the earliest stages, as might have been expected, there is 

 little of importance to record, the resemblance to ordinary birds being 

 very close. One interesting point must, however, be mentioned, 

 although it has no bearing upon the origin of birds. Tn a stage 

 corresponding with a chick of about the sixth day of incubation there 

 is a distinct operculum or gill-cover extending back from the hyoid 

 arch over the 2nd and 3rd visceral clefts. As far as I am aware no 

 such structure has been found in any vertebrate animal above the 

 Amphibia. 



The feathers first make their appearance when the embryo is about 

 60 mm. long and corresponds in its general characters with a chick of 

 the 8th-9th day. They do not appear evenly all over the body, but as 

 a comparatively narrow tract along the middle of the back and. after- 

 wards spreading on to the thighs. Later a tract appears on each 

 side of the belly and smaller tracts on the wings, all being separated 

 by well marked featherless spaces. Even in the adult the most 

 important of these spaces can be traced. 



In the adult there is a loose fold of skin on the anterior border 

 of the wing between the upper arm and the fore- arm, and a similar 

 fold on its posterior aspect between the upper arm and the body. 

 These obviously correspond to the alar membrane so characteristic of 

 ordinary birds. Moreover the adult has a well-marked series of 

 wing-quills covered by regularly arranged upper coverts. 



These facts certainly seem to indicate that the ancestors of 

 the Kiwi had the interrupted pterylosis or feather-arrangement 

 characteristic of CarinatEe, and that their fore-limbs were true wings. 



A minor circumstance which appears to point to the same 

 conclusion is the fact that a sleeping Kiwi assumes precisely the 

 same attitude as an ordinary carinate bird, the head being thrust 

 under the side feathers between the body and the upwardly-directed 

 elbow. 



The development of the wing and of the parts in connection 

 with it is also interesting. At an early stage the fore-limb ends in a 

 three-toed paw, the digits represented being the 1st, 2nd and 3rd : 

 later on the 1st and 3rd digits cease to grow and the fore -limb 

 assumes the form of an ordinary bird's wing with a greatly elongated 

 second digit and small first and third digits. Still later the 1st and 

 3rd digits disappear as distinct structures and the wing becomes the 

 small one-fingered organ characteristic of the adult. 



The skeleton of the wing shows similar changes : at first there 

 are five distinct carpals and three metacarpals. As growth goes on 

 the carpals of the lower or distal row unite with the 2nd and 3rd 

 metacarpals, exactly as in existing birds. The upper or proximal 

 carpals may either unite with the carpo-metacarpus thus formed or 



