236 THE VOYAGE OF H.M.S. CHALLENGER. 



It will be noted that I failed to observe any peculiarity in respect either of the 

 muscular or of the respiratory organs which would serve to explain the power which 

 tlie Penguins possess of remaining submerged for a considerable period of time. 

 This faculty is more probably due to a physiological adaptation of these Ijirds to the 

 necessities of their peculiar mode of life, rather than to any structural modification of the 

 organs which are affected thereby. Mr. Murray* states that a rock-hopper Penguin 

 {Eudyptes chrysoconie), placed in a basket and submerged, " was dead in one minute and 

 thirty seconds," from which we may conclude, considering the great vitality of these 

 birds, that the period during which they usually remain under water when diving is 

 considerably less. From observations made by myself with regard to the length of time 

 which the diving birds of our own coasts (Guillemots, &c.) remain under water, it seems 

 that the duration of each submersion varies from one minute thirty seconds to one 

 minute forty-five seconds, and the length of time during which the Penguins can remain 

 under water is apparently somewhat less. In the Guillemots, as in the Penguins, there is 

 a total absence of any structural modification which would account for the possession of 

 this faculty, which therefore in both cases appears rather to depend upon functional than 

 upon structural modification. 



In respect of the urinary and genital organs, the Penguins have their kidney divided 

 into two lobes, while the male and female organs resemble those of birds in general, the 

 latter presenting the usual atrophy of the ovary and oviduct of the right side. 



The cutaneous system of the Spheniscidse is thoroughly characteristic of the group, 

 and differs from that of every other group of birds, in respect of the uniform distribution 

 of the feathers over every part of the integument, and in the consequent absence of the 

 bare tracts or apteria met with in other birds. The feathers each possess an " aftershaft," 

 the structure of which is similar to that of the feather itself. The " remiges " or quill 

 feathers are not distinguishable from the surrounding feathers ; l^ut the " rectrices " or 

 quill feathers of the tail are clearly diff'erentiated. These cutaneous peculiarities were 

 long since recognised in Aptenodytes patagoniciis and in Spheniscus demersiis, by 

 Nitzsch,^ and I have now confirmed and extended the observation to every sjiecies of 

 Penwuin which I have dissected. The oil glands in the Spheniscidse are of large size, 

 and the duct of each terminates on the cutaneous surface by means of a single orifice. 



Along with the skin it is convenient to direct attention to the great develojDment of 

 the subcutaneous fatty layer of the Penguins, as compared with other birds. This layer 

 far exceeds in thickness that of the corresponding structure in the members of any other 

 o-roup of birds, and recalls to mind the fatty deposit or "blubber" of the Seals and 

 Cetaceans. In the Penguins, as in the mammals just named, this deposit of fat appears 

 to act as a non-conductor of heat, and serves to equalise the temperature of the bird, 



^ Sclater, Challenger Reports, Zoology, part viii. p. 1.32. 



' Pterylography, Ray Soc, edited by P. L. Sclater, F.R.S., p. 154. 



