G II. W. MARETT TIMS. 



naked, darkly pigmeuted skin area, such as Mr. Beddard has figured arid described 

 (3) as present, and of systematic importance, in the Otariidse. 



Perhaps one of the most interesting points in the external features is what I 

 think must be regarded as a vestige of an external ear. lu a very early embryo, 

 situated just behind the eye is a somewhat circular depression (PI. I., figs. 2 and 3), the 

 upper and posterior margin of which is sharply defined. Arising from the bottom of 

 this depression, rather towards the posterior part, is a minute, filiform, forwardly 

 directed, elevation with a small dark speck at its apex. Whether it is an aperture 

 or not I cannot say, but I was unable to insert a bristle into it. This structure was 

 bi-lateral, though more distinct on the right side. 



It corresponds so closely to the description given by Howes (4) of the vestiges 

 of the external ear in two of the Cetacea that I cannot refrain from quoting his words. 

 In a fetal porpoise 22 inches in length was found the external auditory aperture an 

 inch and a quarter behind the eye, into which a fine bristle could be passed. " Over- 

 hanging this aperture was a filamentous process of the integument which measured a 

 quarter of an inch in length, its pointed extremity being turned forwards, while behind 

 it became somewhat broadened, fading off into that covering the head." 



Still more similar is the description given of the external ear in a fetal Beluga, 

 13 inches in length. Howes says (p. 468) that "The external ear opens, in this 

 creature, a little above and three-quarters of an inch behind the eye by a minute 

 slit-like aperture, somewhat cresceutic in shape, and having its concavity turned 

 forwards. There projects out of this aperture a delicate filamentous process, having 

 the same general appearance as that observed in the porpoise, save that it is more 

 slender and appears to spring from the integument forming the posterior lip of the 

 aperture rather than altogether behind it." I think there can be no doubt that the 

 structure present in this fetal seal is the vestige of an external ear, and it is 

 interesting to note the close agreement which exists in the last traces of this organ 

 in animals of different classes, which have undergone so many similar structural 

 alterations in adaptation to their aquatic habit. 



Limbs. The development of the limbs naturally invites attention on account 

 of their adaptive modifications, and it has already been examined to some extent in 

 this connection by Professor Leboucq (7). He, however, had a smaller amount of 

 material at his disposal, and I think it is possible to add some additional points of 

 interest to his published account. The first thing that strikes the observer is the 

 precocious development of the hind limb. In fig. 1 the hind limb is as long, if not 

 slightly longer, than the fore limb. With the growth of the embryo the total length 

 of the latter soon exceeds that of the former, as is seen by a reference to figs. 4, 5, G. 

 This increase is due to an elongation of the femoral and crural segments, since it is not 

 until the embryo reaches a body length of about 144 mm. (No. 16) that the length of 

 the pes begins to exceed that of the manus, and even then there are individual 

 instances in which this is not the case. 



