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



the limb is equal to one-half of the length of the trunk (index, '50). The ratio of 

 growth of the fore limb in the penguin is continuous and progressive in relation to the 

 ratio of growth of the trunk. 



Towards the end of the third week it measures one-half of the length of the trunk 

 (index, 21st day, '50), and at the end of incubation it measures two-thirds (index, - 69) of 

 the length of the trunk. 



In the duck, on the other hand, the length at first increases relatively to the trunk, 

 attaining in one specimen, at the end of the third week, a maximum ratio of over two- 

 thirds (index, 19th day, "67) ; but thereafter it slowly loses ground, and at the close of 

 incubation the fore limb is less than one-half the length of the trunk. 



4. Hind Limb. 



A. Absolute Length. In the penguin at the 12th day of incubation the hind 

 limb is also one-fourth of the length of the hind limb of the duck, the ratio being very 

 similar to that between the upper limbs of the two animals. In the penguin's limb, 

 however, growth is more rapid, with the result that at the end of the third week the 

 hind limb has reached a length equal to nearly one-half of the length of the hind 

 limb of the duck of corresponding age, and at the end of incubation it is rather more 

 than half as long as the corresponding part in the duck. 



5. Ratio of Length of Lower Limb to that of the Trunk. 



At the 12th da} 7 in the penguin the length of the lower limb is approximately 

 one-third of the length of the trunk (index, '34), but the rate of growth is more rapid, so 

 that at the end of incubation it is nearly as long as the trunk (index, 28th day, '82). 



In the duck the limb at 12 days is rather more than two-thirds of the length of 

 the trunk (index, 71), at the 18th day it is nearly as long as the trunk (index, - 92), 

 and thereafter it continues to increase at a rate relatively rather greater than the trunk, 

 so that at the end of the third week it becomes actually longer (index, 22ud day, 1'13), 

 and retains this superiority to the end of incubation. 



In this respect, i.e. in the rate of growth from the 1 8th day, it is the exact reverse 

 of the fore limb it continues to increase in length relatively to the trunk, whereas the 

 fore limb actually shows a relative decrease. 



ANALYSIS OP RESULTS. 



Among the four limbs examined there are, therefore, two types of development. 



First, there is a progressive type, and to this the development of the fore and hind 

 limbs of the penguin and of the hind limb of the duck belongs. 



Second, there is a partially regressive type, and to this the development of the fore 

 limb of the duck belongs. 



(ROY. soc. EDIN. TRANS., VOL. XLVII., 236.) 



