674 



SCIENCE. 



[N. S. Vol. IV. No. 97. 



all such evidence as is available, tliat the 

 evolutionary history in these early times 

 was comparatively rapid. 



To recapitulate, if we represent the his- 

 tory of animal evolution by the form of a 

 tree, we find that the following growth took 

 place in some age antecedent to the earliest 

 fossil records, before the establishment of 

 the higher Phyla of the animal kingdom. 

 The main trunk representing the lower 

 Protozoa divided, originating the higher 

 Protozoa ; the latter portion again divided, 

 probably in a threefold manner, originating 

 the two lowest Metazoan Phyla, constituting 

 the Coelentera. The branch representing 

 the higher of these Phyla, the I^ematophora, 

 divided, originating the lower Coelomate 

 Phyla, which again branched and originated 

 the higher Phyla. And, as has been shown 

 above, the relatively ancestral line, at every 

 stage of this complex history, after origina- 

 ting some higher line, itself continued down 

 to the present day, throughout the whole 

 series of fossiliferous rocks, with but little 

 change in its general characters, and prac- 

 tically nothing in the way of progressive 

 evolution. Evidences of marked advance 

 are to be found alone in the most advanced 

 groups of the latest highest products— the 

 Phyla formed by the last of these divisions. 



It may be asked how is it possible for the 

 zoologist to feel so confident as to the past his- 

 tory of the various animal groups. I have 

 already explained that he does not feel this 

 confidence as regards the details of the his- 

 tory, but as to its general lines. The evi- 

 dence which leads to this conviction is based 

 upon the fact that animal structure and 

 mode of development can be, and have been, 

 handed down from generation to generation 

 from a period far more remote than that 

 which is represented by the earliest fossils ; 

 that fundamental facts in structure and de- 

 velopment may remain changeless amid end- 

 less changes of a more general character ; 

 that especially favorable conditions have 



preserved ancestral forms comparatively 

 unchanged. Working upon this material, 

 comparative anatomy and embryology can 

 reconstruct for us the general aspects of a 

 history which took place long before the 

 Cambrian rocks were deposited. This line 

 of reasoning may appear very speculative 

 and unsound, and it may easily become so 

 when pressed too far. But applied with 

 due caution and reserve, it may be trusted 

 to supply us with an immense amount of 

 valuable information which cannot be ob- 

 tained in any other way. Furthermore, it 

 is capable of standing the very true and 

 searching test supplied by the verification 

 of predictions made on its authority. Many 

 facts taken together lead the zoologist to 

 believe that A was descended from C 

 through B ; but if this be true, B should 

 possess certain characters which are not 

 known to belong to it. Under the inspira- 

 tion of hypothesis a more searching investi- 

 gation is made, and the characters are 

 found. Again, that relatively small amount 

 of the whole scheme of animal evolution 

 which is contained in the fossiliferous rocks 

 has furnished abundant confirmation of the 

 validity of the zoologist's method. The 

 comparative anatomy of the higher Verte- 

 brate Classes leads the zoologist to believe 

 that the toothless beak and the fused cau- 

 dal vertebrae of a bird were not ancestral 

 characters, but were at some time derived 

 from a condition more conformable to the 

 general plan of vertebrate construction, 

 and especially to that of reptiles. Numer- 

 ous secondary fossils prove to us that the 

 birds of that time possessed teeth and 

 separate caudal vertebrae, culminating in 

 the long lizard-like tail of Archseopteryx. 



Prediction and confirmation of this kind, 

 both zoological and paleontological, have 

 been going on ever since the historic point 

 of view was adopted by the naturalist as 

 the outcome of Darwin's teaching, and the 

 zoologist may safely claim that his method. 



