370 H. N. Hutchinson — Skeleton of Diplodocus Camegiei. 



This can best be illustrated by means of a pocket-handkerchief. 

 Place it on an extended left arm, with part hanging over one side 

 near the body. Then put the right hand under it with the fingers 

 placed at right angles to the arm. They project in a sharp edge. 

 Now turn the hand round through 90 degrees of arc, and this awkward 

 projecting edge vanishes. It is most instructive to compare with 

 this the articulation seen in JVesiosaurus, Pareiasaurus, Iguanodon, 

 Thescelosaurus, and many other forms. They all confirm the idea of 

 an oar, rather than a pendulum (see p. 369, Pig. 9, a, b, c). 



The writer has consulted on this point a London University 

 Professor of Engineering, who confirms the views here expressed. 



Physiology a Useful Guide. 



To ail students of evolution it is important to bear in mind, as 

 a guiding principle, the one which Sir Richard Owen always kept 

 steadily in view, that anatomy and physiology go hand in hand. 

 There is a kind of correlation between them. The evolutionist, in 

 pondering over the development of animal life on the earth from the 

 earliest geologic periods to the present day, perceives on reflection 

 that every great advance in structure is based not only on anatomical 

 improvements but also on physiological changes. Thus, the mammal 

 takes the place of the reptile in the order of evolution, and exhibits a 

 heart with four chambers, compared with the reptiles' three; and the 

 reason for this is that the mammal is intended to win a higher place 

 for himself. He must be stronger and swifter, and more intelligent 

 than the reptile. His limbs are therefore stronger, and his brain 

 more active. Hence he requires an improved apparatus. Nature, the 

 great designer, acts in much the same way as an engineer. It is as 

 if an engineer had to deal with an old out-of-date motor-car. He 

 wants to improve it and make it run better and faster. So he takes 

 out the old three-cylinder engine and replaces it by one with four 

 cylinders. He also strengthens the chassis here and there, and thus 

 obtains the results that have been slowly arrived at. So nature 

 discarded the old reptilian heart and replaced it by one of greater 

 power to pump the blood to all parts of the body. 



Although land mammals differ very much among themselves as 

 regards powers of progression, they are on the whole better endowed 

 for this purpose than either the amphibia or reptilia. This is largely 

 due to theirgreater activity associated with the relatively more efficient 

 circulatory and respiratory organs. Warm and well-oxygenated blood 

 at a more or less constant temperature circulates freely all over the 

 body, endowing the limbs with considerable power of activity. A like 

 activity either of brain or muscle is not to be expected in the Amphibia 

 or the lieptilia. The skeleton of the mammal is designed with a view 

 to efficient walking and running. Now Diplodocus being a reptile, 

 we are not entitled to expect that its limbs should be arranged on 

 the mammalian plan. Our study of its limb-bones confirms this 

 anticipation. Its character, we hope, has been vindicated ; it no 

 longer can be said to have played a part for which it was not 

 intended by nature. 



