230 DR D. WATERSTON AND DR A. CAMPBELL GEDDES ON EMBRYO PENGUINS 



somite. The folds approached one another closely at the posterior end, and in that 

 region they enclosed a clear area, shaped like an arrow head, in which lay the expanded 

 posterior end of the notochord. The end of the notochord projected backwards beyond 

 the medullary folds in the form of a bulbous extremity. Behind it there was no 

 distinct evidence of a primitive streak. The whole of the posterior portion was 

 enclosed in a clear oval area. The somites were well formed, and their internal 

 structure showed them to consist of a clear central portion and a periphery or 

 cortex arranged in columns radiating outwards. 



At the outer margin of the somites was a clear area in which lay a narrow darker 

 line, extending along the side from the third anterior somite backwards to beyond the 

 hinder somites. 



In position this structure corresponds to the primitive cardinal vein. 



The neural folds showed evidence of segmentation, being constricted opposite the 

 centre of the somites, and they were united about the middle. The specimen described 

 was one said to be of the sixth day, and the subsequent specimens, which showed stages 

 of gradual advance, were in harmony with this statement. 



If these dates be accepted, it is obvious that the early changes in the penguin 

 embryo are very much slower than the corresponding changes in the chick, for the 

 same degree of development is shown in the chick of 40-44 hours. 



Specimens VII., VIII, IX., and X. (fig. 6). — Labelled 7-11 days. — These 

 specimens showed that the next stages of development are very similar to 

 corresponding stages in the development of the chick, and do not require detailed 

 description, except in so far as they show differences from it. The head and trunk 

 show gradual increase in length and in thickness. 



At the hinder end of the notochord a dark area shaped like a spear-head persists 

 for some time, but eventually becomes merged in the hinder end of the trunk. 



Figs. 7, 8, and 9, which illustrate the development of the duck at 5, 6, and 7 days, 

 are introduced for comparison with fig. 6, which is a photograph of a penguin embryo 

 labelled as 8 days. 



Section II. — Kate of Growth of the Trunk and Limbs from the 



Twelfth Day onwards. 



Our observations were directed first to an examination and measurement of the 

 developing trunk and limbs. 



The observations begin with the twelfth day of incubation, which is the date of 

 appearance of the limb buds upon the surface of the body. 



The details of the measurements are recorded in the appended table (Table 

 No. I.). 



