The Worst Journey in the World/Appendix
APPENDIX
PROFESSOR COSSAR EWART'S REPORT
"It was a great disappointment to Dr. Wilson that no Emperor Penguin embryos were obtained during the cruise of the Discovery. But though embryos were conspicuous by their absence in the Emperor eggs brought home by the National Antarctic Expedition, it is well to bear in mind that the naturalists on board the Discovery learned much about the breeding habits of the largest living member of the ancient penguin family. Amongst other things it was ascertained (1) that in the case of the Emperor, as in the King Penguin, the egg during the period of incubation rests on the upper surface of the feet protected and kept in position by a fold of skin from the lower breast; and (2) that in the case of the Emperor the whole process of incubation is carried out on sea ice during the coldest and darkest months of the antarctic winter.
"After devoting much time to the study of penguins Dr. Wilson came to the conclusion that Emperor embryos would throw new light on the origin and history of birds, and decided that if he again found his way to the Antarctic he would make a supreme effort to visit an Emperor rookery during the breeding season. When, and under what conditions, the Cape Crozier rookery was eventually visited and Emperor eggs secured is graphically told in The Winter Journey. The question now arises, Has 'the weirdest bird's-nesting expedition that has ever been made' added appreciably to our knowledge of birds?
"It is admitted that birds are descended from bipedal reptiles which flourished some millions of years ago—reptiles in build not unlike the kangaroo. From Archaeopteryx of Jurassic times we know primeval birds had teeth, three fingers with claws on each hand, and a long lizard-like tail provided with nearly twenty pairs of well-formed true feathers. But unfortunately neither this lizard-tailed bird, nor yet the fossil birds found in America, throw any light on the origin of feathers. Ornithologists and others who have devoted much time to the study of birds have as a rule assumed that feathers were made out of scales, that the scales along the margin of the hand and forearm and along each side of the tail were elongated, frayed and otherwise modified to form the wing and tail quills, and that later other scales were altered to provide a coat capable of preventing loss of heat. But as it happens, a study of the development of feathers affords no evidence that they were made out of scales. There are neither rudiments of scales nor feathers in very young bird embryos. In the youngest of the three Emperor embryos there are, however, feather rudiments in the tail region,—the embryo was probably seven or eight days old—but in the two older embryos there are a countless number of feather rudiments, i.e. of minute pimples known as papillae.
"In penguins as in many other birds there are two distinct crops of feather papillae, viz.: a crop of relatively large papillae which develop into prepennae, the forerunners of true feathers (pennae), and a crop of small papillae which develop into preplumulae, the forerunners of true down feathers (plumulae).
"In considering the origin of feathers we are not concerned with the true feathers (pennae), but with the nestling feathers (prepennae), and more especially with the papillae from which the prepennae are developed. What we want to know is, Do the papillae which in birds develop into the first generation of feathers correspond to the papillae which in lizards develop into scales?
"The late Professor Assheton, who undertook the examination of some of the material brought home by the Terra Nova, made a special study of the feather papillae of the Emperor Penguin embryos from Cape Crozier. Drawings were made to indicate the number, size and time of appearance of the feather papillae, but unfortunately in the notes left by the distinguished embryologist there is no indication whether the feather papillae were regarded as modified scale papillae or new creations resulting from the appearance of special feather-forming factors in the germ-plasm.
"When eventually the three Emperor Penguin embryos reached me that their feather rudiments might be compared with the feather rudiments of other birds, I noticed that in Emperor embryos the feather papillae appeared before the scale papillae. Evidence of this was especially afforded by the largest embryo, which had reached about the same stage in its development as a 16-days goose embryo.
"In the largest Emperor embryo feather papillae occur all over the hind-quarters and on the legs to within a short distance of the tarsal joint. Beyond the tarsal joint even in the largest embryo no attempt had been made to produce the papillae which in older penguin embryos represent, and ultimately develop into, the scaly covering of the foot. The absence of papillae on the foot implied either that the scale papillae were fundamentally different from feather papillae or that for some reason or other the development of the papillae destined to give rise to the foot scales had been retarded. There is no evidence as far as I can ascertain that in modern lizards the scale papillae above the tarsal joint appear before the scale papillae beyond this joint.
"The absence of papillae below the tarsal joint in Emperor embryos, together with the fact that in many birds each large feather papilla is accompanied by two or more very small feather papillae, led me to study the papillae of the limbs of other birds. The most striking results were obtained from the embryos of Chinese geese in which the legs are relatively longer than in penguins. In a 13-days goose embryo the whole of the skin below and for some distance above the tarsal joint is quite smooth, whereas the skin of the rest of the leg is studded with feather papillae. On the other hand, in an 18-days goose embryo in which the feather papillae of the legs have developed into filaments, each containing a fairly well-formed feather, scale papillae occur not only on the foot below and for some distance above the tarsal joint but also between the roots of the feather filaments between the tarsal and the knee joints. More important still, in a 20-days goose embryo a number of the papillae situated between the feather filaments of the leg were actually developing into scales each of which overlapped the root (calamus) of a feather just as scales overlap the foot feathers in grouse and other feather-footed birds.
"As in bird embryos there is no evidence that feather papillae ever develop into scales or that scale papillae ever develop into feathers it may be assumed that feather papillae are fundamentally different from scale papillae, the difference presumably being due to the presence of special factors in the germ-plasm. Just as in armadillos hairs are found emerging from under the scales, in ancient birds as in the feet of some modern birds the coat probably consisted of both feathers and scales. But in course of time, owing perhaps to the growth of the scales being arrested, the coat of the birds, instead of consisting throughout of well-developed scales and small inconspicuous feathers, was almost entirely made up of a countless number of downy feathers, well-developed scales only persisting below the tarsal joint.
"If the conclusions arrived at with the help of the Emperor Penguin embryos about the origin of feathers are justified, the worst journey in the world in the interest of science was not made in vain."
END OF VOLUME ONE
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