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



METHODS OF EXAMINATION. 



The earlier specimens were prepared for examination by being stained in borax 

 carmine or alum carmine and mounted entire. Duplicate specimens for examination 

 by section were not available. The later specimens were cleared so far as possible, 

 but owing to the long immersion in formalin the clearing did not yield very satisfactory 

 results. A figure illustrating the development of the limb bones is included among the 

 illustrations (fig. 26). The decalcifying action of the formalin has, unfortunately, 

 made any definite statements as to date of appearance and order of appearance of the 

 ossific centres impossible, and we have had to content ourselves with the negative 

 observation that no unusual or abnormal processes or sequences were to be observed, 

 although such were looked for as carefully as the material available would permit. 



In order to carry out a comparison regarding the dates of acquisition of the external 

 adult features and the progressive development of the limbs and trunk during the 

 later stages of development, we found it necessary to provide a control by carrying out 

 observations on the same lines upon the embryo of another genus of birds. 



Data for this purpose were not available in the literature, and we therefore prepared 

 and examined, by methods identical with those used for the penguins, a series of duck 

 embryos at every 24 hours of incubation. The period of incubation in the duck (28- 

 30 days) approximates sufficiently closely to that of the penguin (30-32 days ?) to 

 enable comparisons to be drawn with accuracy between embryos of corresponding age 

 taken at each 24 hours. 



The data which we obtained appear to be new, and we have, therefore, included an 

 account of the external form and the measurements of the embryo-duck with those of 

 the penguins. 



SECTION I. EARLY STAGES OF DEVELOPMENT. 



EMBRYOS SHOWING EARLY STAGES, COMPRISING SPECIMENS UP TO THE TWELFTH DAY. 



Specimen I. In the first of these, which was the youngest specimen examined, 

 there was an oval area pellucida measuring 3 mm. in length on the surface of the 

 blastoderm. This specimen illustrates the earliest stage after the close of segmentation 

 before the formation of the primitive streak, and it closely resembles in size and shape 

 the corresponding area in the ovum of the chick and the duck. No area opaca could be 

 made out, nor was there any sign of the embryonic shield. The shape of the area 

 pellucida is comparable to that seen in the blastoderm of the chick at about 18 hours, 

 but in the absence of primitive streak and embryonic shield it resembles the chick 

 blastoderm at the commencement of segmentation. 



Specimen II. (fig. 1). The second specimen showed a more advanced stage. The 

 germinal area was somewhat pear-shaped. At its wider end was a narrow, semi- 



(ROY. HOC. EDIN. TRANS., VOL. XLVII., 228.) 



