554 



SCIENCE. 



hind limbs, it is also extended between the fingers of the 

 fore limbs. Possibly in the early flying efforts of bats 

 the fingers were extended in such a manner as to render 

 any accidental growth of skin between them an advan- 

 tage. Differences in the locomotive habits, and in the 

 foot development, of the progenitors of flying reptiles and 

 flving mammals, may account for this greater extension 

 of the flying membrane in the case of the latter. Na'- 

 urally such an advantage was seized upon and improved 

 by natural selection. The membrane ex'ended to the tips 

 of the firgers, the fingers themselves grew much longer, 

 and in time the fore limb lost all its powers as a walking 

 organ, but became developed into an efficient flying or- 

 gan, Bats, by this specialization of their fore limbs, 

 ceased to be quadrupeds, though they never became true 

 bipeds. Sleep and flight constitute the measure of their 

 existence. 



Thus the development of all flying vertebrates other 

 than birds pursued the same general course. It began 

 with the extension of the skin of the sides, so as to serve 

 for parachute motion ; and ended with an extension of 

 the fingers of the fore limbs, an extension ot the mem- 

 brane to the tips of these elongated fingers, and a flying 

 motion of these limbs. In necessary connection with 

 these were concomitant internal changes, the whole anat- 

 omy of the animal becoming adapted to its flying habits. 



But in the development of bird flight quite a different 

 mode of evolution appears. Flight is here attained not 

 by a special adaptation of the skin, but of the dermal 

 covering. This covering was probably not the hair in its 

 full modern sense. Ifcwas a primitive derivation from the 

 reptilian scale, which secondarily became the avian feather 

 and the mammalian hair. The feather of the bird agrees 

 with the scale of the reptile in being developed in little 

 hillocks upon the skin. The hair of the mammal devel- 

 oped in closed follicles within the skin. There thus has 

 been a specialization in both, with the production of a 

 change in the terminal character of the feather and in the' 

 dermal origin of the hair. 



The progenitors of birds were either land or tree dwell- 

 ing reptiles; most probably the latter. We have seen the 

 extreme improbability that any leaping motion from the 

 earth developed into a flight. We have also seen how 

 natural it is for animals to leap from the limbs of trees, 

 and that, in several modern instances, a degree of aerial 

 support hai been thus developed. But in such a leaping 

 motion it is highly probable that some animals would 

 make other efforts for support in the air besides the hori- 

 zontal extension of their limbs. The swimming motion 

 is a very natural one. It is naturally adopted by all 

 land animals which fall into the water, and the webbed 

 feet of swimming birds have been produced by it in the 

 same manner as the webbed fingers of flying bats. Let 

 us now consider some early animal, so far advanced be- 

 yond the reptilian ranks as to have become warm blooded, 

 and covered with the primitive form of hair, arboreal in 

 its habits, and accustomed to make long leaps from limb 

 to limb. It is by no means improbable that some such 

 animals would seek to swim in the air. A rapid motion 

 of the fore limbs could not but aid in keeping the body 

 horizontal, and if these limbs were covered with thick 

 hair this must aid in breaking the fall of the animal. 

 Any such habit could have but one result. A thicker 

 hairy covering of the fore limbs, and even of the whole 

 body, would prove an advantage to the animal, and these 

 thickly matted hairs would tend to spread laterally, pre- 

 cisely as we find in the tails of Flying Squirrels and 

 Phalangers. A still further advantage would be gained 

 were these hairs rough instead of smooth on their edges, 

 so as to cling together, and prevent the air from passing 

 between them. 



Such a swimming motion, performed by the fore limbs 

 principally, — the hind limbs being the leaping organs, — 

 and aided by the lateral outgrowth, and the " felting" of 

 rough edged hairs, would, from its inception, be more 



than a parachute motion. It would be incipient flight 

 from the first, a swimming in the a ; r. The essential ad- 

 vantages gained by longer and longer leaps must tend to 

 preserve any favorable conditions of the hair, and we 

 can readily conceive the rough edges of the hairs ex- 

 tending into interlocking feathery exransiens. In fact it 

 is not difficult to imagine the slow evolution of true 

 feathers in this manner, since every incipient approach to 

 the feather must prove advantageous to the animal in its 

 aerial motion. 



But every better adapted movement of the fore limbs 

 must prove similarly advantageous. Not only any varia- 

 tion from hairs towards feathers would be advantageous, 

 but also any variation from a swimming towards a flying 

 movement of the fore limbs. Of course the process 

 must have been a slow one. It was necessarily slow also 

 in the case of the bat and the Pterodactyl. But in all 

 these cases every increment of variation from leaping to- 

 wards flying was advantageous, so that there was no 

 hindrance to a continual evolution towards full powers of 

 flight. 



But the development of the fore limbs into feathered 

 wings unfitted them more and more for walking organs. 

 The slowly developing bird must have trusted more and 

 more to its hind limbs for support. Its arboreal habit 

 developed the toes of these limbs into grasping organs. 

 The original quadruped in time became a true biped, 

 with a foot specially adapted to grasp the rounded sur 

 faces of the limbs of trees, and so changed in position 

 as to fall under the centre of gravity of the body. Hairs 

 became feathers, the bones ot the fore limbs aborted in 

 part and became wing bones, and the original tree leap- 

 ing reptile became a flying bird. 



We may close with a very brief further consideration. 

 In the first place it is highly probable that only quite 

 small animals first gained this flying habit. Considerable 

 weight would hinder its development. But after it was 

 once gained there would be no special hindrance to in- 

 crease in size in the newly evolved species. Yet a very 

 great increase in size would so greatly increase the mus- 

 cular effort necessary to flight that the larger birds would 

 most likely spend a considerable portion of their time 

 upon the earth. And in many cases the increased weight 

 w hich is apt to arise from diminution of muscular exer- 

 cise might render a resumption of the flying habit im- 

 possible. Such birds would lose their aerial powers, and 

 become true land bipeds. We may ascribe the land resi- 

 dence, and the aborted wings, of the Ostrich, Cassowary, 

 &c, to some such secondary process of evolution. On 

 the other hand, many virtually land birds have become 

 so by an adaptation to food in the obtaining of which 

 flight was no advantage. Organs not used soon lose 

 their muscular vigor, their size decreases, and gradual 

 abortion takes place, unless adaptation to some new func- 

 tion gives them a special development in this new direc- 

 tion, and checks their tendency to disappear. 



II. 



STONE IMPLEMENTS IN THE DRIFT.* 



By Watson C. Holhrook. 



Many stone implements have been found deeply buried 

 in the clay and gravel of Whiteside county, Illinois. 

 Mindful of the many sources of error, and fully conscious 

 of the many grave and serious questions involved, I have 

 endeavored to examine with care and attention every one 

 of the finds. The first is a black chest spear head about 

 five inches long found incased in a block of granular 

 stalagmite. This specimen was found in a light-blue 

 clay. Above this clay was an alluvial deposit about five 

 feet thick. Some pre-historic man must have left.his 

 spear head in a cave or hid it in a fissure cf rock. Layer 

 after layer of stalagmite was found. The spear's head 



*A. A. A. ?., Cincinnati, Ml. 



