646 



NA TURE 



[October 31, 1901 



Again, as suggestive of prejudice, we must take the 

 strongest exception to the author's use of the expression 

 "than might have been anticipated" in connection with 

 the affinities between pterodactyles and dinosaurs. What 

 right had anybody to form '• anticipations" ? 



If the author really intends to imply that birds and 

 pterodactyles are divergent and specialised branches 

 from groups of reptiles which cannot yet be identified (at 

 all events in the latter case) with any approach to cer- 

 tainty, we can agree with him. But this by no means 

 iinplies any intimate relationship between the two 

 branches in question, the structure of the limbs of which is 

 alone amply sufficient, in our opinion, to demonstrate their 

 totally different origin. In urging an affinity between 

 birds and pterodactyles, Prof. Seeley, in addition to the 

 (may we say superficial ?) resemblances between their 

 skulls and brains, lays stress on the fact that both have 

 pneumatic bones. This feature is taken as an indication 

 that pterodactyles probably possessed warm blood, from 

 which is drawn the further inference that they were also 

 furnished with a four-chambered heart. Even if the 

 first inference be well founded, the second by no means 

 follows, the author himself quoting the fact that the 

 blood of the tunny has a temperature of 90°. And even 

 if pterodactyles were warm-blooded and furnished with 

 an avian type of heart, we should be none the more 

 inclined to admit their affinity with birds. 



Apparently the author takes no account of similar 

 modes of life leading to the development of superficially 

 similar bodily structure in totally different groups of 

 animals, and the consequent " convergent " resemblance 

 between them. And if this be so, his premises are so 

 widely different from those on which the investigations of 

 others are based that it is little wonder irreconcilable 

 diversity of view results. 



An instance of th.s nature occurs on p. 219, where we 

 find the statement that " a few characters of ornithosaurs 

 are regarded as having been acquired, because they are 

 not found in any other animals, or have been developed 

 only in a portion of the group." In one sense all characters 

 are acquired ; but the use which the author makes of the 

 term "acquired characters " does not correspond with its 

 ordinary scientific acceptation. From this we may 

 perhaps infer that in other instances the signification 

 attached to terms is different from that usually in vogue — 

 which would account for much. 



It is not, however, solely in regard to the affinities of 

 these reptiles, as we still take leave to call them, that the 

 author differs so much from current views. He likewise 

 attributes to pterodactyles a bodily form quite unlike that 

 with which they are generally credited ; and one, it may 

 be said, which makes them the most grotesque and 

 bizarre creatures that ever walked this earth. But could 

 they walk at all, as thus restored ? is a question which can 

 scarcely fail to occur to those who look on these wonderful 

 pictures. In most or all other restorations, as in the 

 plate by .Smit in Hutchinson's " Extinct Monsters," 

 pterodactyles, when not flying, are shown crawling on 

 rocks or cliffs, or sitting up on their hind legs on some 

 prominence preparatory to taking flight. Prof. Seeley 

 will, however, have nothing to say to such crouching 

 attitudes, and represents the creatures standing on all 

 fours, with the greatly elongated wing-finger bent back 

 NO. 1670, VOL. 64] 



alongside the fore-arm and projecting above the hind- 

 cjuarters, and the wing folded like an inverted Chinese 

 sun-shade. Whether such slender hind-limbs as are 

 shown in the restoration are capable of supporting the 

 weight of the body in this position we will not pause to 

 inquire. Our difficulty is in connection with the fore- 

 limb, the raising of which would apparently cause 

 the wings to strike against the ground at every 

 step, even if they did not become entangled with the 

 hind-legs. iSIoreover, the creature is represented as 

 actually standing on the joint between the metacar- 

 pus and the wing-finger, and as this joint must certainly 

 have been a highly delicate and complex structure, it 

 appears impossible to conceive how it could have escaped 

 injury in walking if carried in the position shown in the 

 restoration. Possibly the author has an explanation of 

 these difficulties, but if so it would have been more 

 satisfactory had it been given to the public. 



To revert, in conclusion, to the main argument of the 

 book, we fully realise the amount of labour that Prof. 

 Seeley has expended on a very difficult subject, and at 

 the same time are prepared to admit the advantage 

 which often accrues to the progress of science from the 

 presentation of opinions widely diffisrent from those 

 generally entertained. Nevertheless, we scarcely think 

 that he will persuade those of his readers whose verdict 

 is worth having to agree with him in regarding pterodac- 

 tyles and birds as in any way near akin, or will convince 

 them that the former creatures are no longer entitled to 

 be classed as reptiles. Aberrant they are, no doubt, but 

 not so much so as, in our opinion, to be excluded from 

 the limits of a class comprehensive enough to embrace 

 such diverse types as dinosaurs, turtles, ichthyosaurs 

 and snakes. As to the alleged relationship between the 

 "dragons of the air" and the egg-laying mammals, we 

 are fain to confess that it requires a greater power of 

 imagination to realise the nature of the affinity than it 

 falls to our own lot to possess. R. L. 



ELEMENTARY DYNAMICS. 

 Theoretical Mechanics : an Elementary Treatise. By 

 W. Woolsey Johnson, Professor of Mathematics, U.S. 

 Naval Academy. Pp. xv-t-434. (New York : John 

 Wiley and Sons. London : Chapman and Hall, Ltd., 

 1901.) Price 3 dollars net. 



THE author states in his preface that "the study of 

 mechanics is here supposed to follow an adequate 

 course in the differential and integral calculus." Hence 

 it is difficult to see how it can appeal to any class of 

 students— at least in this country— especially as, in 

 addition to both branches of the calculus, the concep- 

 tions of geometry of three dimensions are also introduced 

 at the outset. The student who has already progressed 

 thus far in mathematics does not require to be introduced 

 to the parallelogram of forces and all the elements of 

 the composition and resolution of coplanar forces and 

 velocities. There is nothing distinctively novel in the 

 work, which is, on the whole, a careful compilation from 

 the works of the best writers on the subject, witliout any 

 acknowledgment of the sources. 



The first two chapters deal with forces acting on a 

 particle, and make free use of the calculus and geometry 



