56 DR D. WATERSTON AND UR A. CAMPBELL GEDDES ON EMBRYO PKNGUINS 



together 5'51 cms. giving a total length of 9*91 cms. The 1'5 cms. of difference (9'91 

 cms. 8 '41 cms.) is accounted for by the marked spinal curves which immediately asserted 

 themselves on extension, a lumbo-thoracic curve ventrally concave, a cervical curve 

 dorsally concave. 



SUMMARY AND CONCLUSION. 



Part 1. Anatomy of the Adult Penguin. 



1. The cervical portion of the vertebral column is possessed of a curve of extra- 

 ordinary convexity which causes the vertebral bodies to form a visible bulging on the 

 front of the neck. This convexity we regard as useful to the birds by increasing water 

 displacement anteriorly and permitting of the head and beak being carried without 

 undue fatigue on the long ocean voyages which the birds undertake. The furcal angle 

 being occupied by the vertebral bodies, the trachea and oesophagus enter the thorax on 

 a plane posterior to the cervical spines. This curvature of the column and arrangement 

 of the viscera is permanent and characteristic of the adult bird. 



2. The arrangement of the fascial layers in relation to the pectoral muscles suggests 

 that the pectoralis major and clavicle are in reality cutaneous structures. It was found 

 impossible from the embryological material at our disposal to prove or to disprove this 

 suggestion. 



Part II. Embryology of the Penguin. 



1. The number of days of incubation is, according to the series of specimens, thirty. 

 This is surprisingly short, and as there are some obvious gaps in the series, we are not 

 prepared to express an opinion as to whether it is correct or not. 



2. The early stages of development are exactly comparable to the corresponding 

 stages of the chick or duck, though, if the dates of our specimens be correct, they take 

 place more slowly. 



3. The later stages of development are exactly comparable to the corresponding 

 stages of the duck except with regard to the down, the fore limb, and the foot. 



4. The foot of the penguin is, throughout its development, exceedingly clumsy and 

 primitive, as is the foot of the adult ; the foot of the duck, from its earliest appearance, 

 assumes a lighter and neater appearance, and is adapted as a paddle, which the foot of 

 the penguin is not. 



5. The fore limb of the penguin is, in its mesoblastic structures, definitely progressive, 

 whereas the mesoblastic portion of the duck's wing is relatively regressive. Both, 

 however, have varied from the ancestral type, but their variation is in opposite direc- 

 tions : the wing of the penguin has required rigidity to subserve its function as a paddle, 

 and it has acquired it, throughout its length. The wing of the duck, on the other hand, 

 has required lightness, and it has acquired it the reduced spread of bone being 

 compensated for by an increased development of feathers. 



(ROY. soc. EDIN. TRANS., VOL. XLVII., 242.) 



