154 DISCOVERY REPORTS 



Structures may be seen in the skin of an embryo duck of about fourteen days' incubation 

 (Lament, 1922, p. 234). They are stated to be the forerunners of the true down, while 

 the large feather filaments are said to give rise to the natal down which precedes the 

 development of the true feathers. 



In the penguin the subsequent history of these small papillae is different. They are 

 no longer visible at the surface by the time the embryo is ready to hatch, and no traces 

 of them are to be found in sections of the skin. Even if they actually abort, their tem- 

 porary presence is of great interest in view of the fact that the epidermis, over which they 

 are scattered, splits up later into a regular pavement of soft scales between the feather 

 filaments (Fig. 6 /, sc). They clearly grow independently of the " scales ", since they pre- 

 cede them, and as their numbers are greater they are not to be regarded as the precursors 

 of the individual " scales ". 



THE CARTILAGINOUS SKELETON 



This was investigated in the early stages of development by means of the Victoria 

 blue staining method for cartilage (van Wijhe, 1902, 1922). Fixation in formalin is 

 necessary for the successful application of this stain, and therefore only the Bouin-fixed 

 material was suitable for its use. The result of using the method on four different stages 

 of the Gentoo embryos is illustrated in Fig. 7. The stages are: a, stage 22; b, stage 26; 

 c, stage 31 ; and e, stage 34. It will be seen that at stage 22 practically no cartilage is 

 laid down. The stain picked out, however, the track of the future vertebral column and 

 it must be presumed that the first cartilage is deposited there. 



More is seen in stage 26 (Fig. y b). In the head region the mass of cartilage in the 

 vicinity of the otocyst, the rudiment of the quadrate and an already strongly developed 

 cartilage supporting the lower jaw (Meckel's cartilage), are all clearly made out. In the 

 body the first cartilages of the limbs make their appearance, namely those that form the 

 scapula, coracoid, humerus, radius and ulna of the fore-limb; and the femur, tibia and 

 fibula in the hind-limb. 



Having once started the cartilaginous skeleton is rapidly built up ; for by the time 

 stage 31 (Fig. 7 c) is reached many additional elements have been laid down. With the 

 development of the beak the premaxilla can be distinguished from the mass of cartilage 

 at the front of the orbit, and continuous with it there runs posteriorly a bar of cartilage 

 out of which is built the interorbital septum — the mesethmoid — and the orbitosphenoid. 

 Immediately behind the orbit is the rudiment of the alisphenoid, a cartilage perforated 

 by the foramen of the fifth cranial nerve. It is temporarily in the shape of an inverted Y, 

 and between the two arms of the Y nearest the back of the head lies the otocyst already 

 firmly enclosed by peri otic cartilages. One arm of the alisphenoid passes under the 

 quadrate and makes contact with another similar cartilage, bearing a foramen, the 

 exoccipital. 



In the body the most conspicuous change lies in the development of some of the digital 

 elements of the rapidly growing limbs. Their exact succession has been carefully de- 

 scribed by Anthony and Gain (19 15), and little need be added to the subject here. It is, 



