August 14, 1896.] 



SCIENCE. 



181 



the fragments enclosed in the oceanic de- 

 posits along its shores, how very imperfect 

 would our knowledge be ! Although the 

 estuarine, swamp and lake formations, 

 which occur on such a grand scale among 

 the rocks of the earth's crust, have pre- 

 served whole chapters in the history of ter- 

 restrial life with wonderful fullness and 

 accuracy, they are all too few and too widely 

 separated to form any complete record. 

 Even in a continuous series of marine de- 

 posits, representing vast periods of time, 

 there are sure to be gaps of greater or less 

 importance in the record. Changes in the 

 depth of water and the character of the bot- 

 tom will drive out one set of forms from 

 that locality and bring in another, which 

 has no genetic connection with the former, 

 which may perhaps return with a renewal 

 of the old conditions. Many groups of or- 

 ganisms are incapable of preservation in 

 the fossil state, except under the rarest con- 

 ditions — conditions which occur so seldom, 

 and so widely separated in space and time, 

 as to render hopeless any attempt to re- 

 construct a continuous story from them. 



The very circumstances under which or- 

 ganisms are preserved in the rocks offer 

 another obstacle to the determination of 

 phyletic series. On examining large col- 

 lections of fossils from several successive 

 horizons, we find that the majority of the 

 species and even of the genera are confined 

 to one or two formations, and that each 

 succeeding fauna is recruited partl}^ by 

 migrations from other regions and partly by 

 the rapid expansion of comparatively few 

 adaptive and plastic types, while most of 

 the forms which were especially well fitted 

 for the older conditions die out under the 

 new. The collections are, of course, largely 

 made up fr'om the abundant and dominant 

 species of each horizon, which frequently 

 are not the ancestors of those which will be 

 dominant in the succeeding one. The sud- 

 den appearance, as it so often seems to be, 



of a fully differentiated group is sometimes 

 due to that cause, sometimes to a migration 

 from some other region. Even in phyletic 

 series which are well-nigh complete there 

 is a tendency for each successive genus to 

 undergo similar cycles of specific variation, 

 and this adds to the confusion, the very 

 completeness of the record increasing the 

 difficulty of its interpretation. 



(2) a second drawback to the paleonto- 

 logical method of inquiry lies in the incom- 

 plete preservation of those organisms which 

 are fossilized. Of plants we find, for the 

 most part, only scattered leaves, rarely the 

 reproductive organs, stems or roots, and 

 often the proper association of the various 

 parts requires the strenuous labor of years. 

 Of animals, except under exceedingly rare 

 circumstances, only the hard parts, teeth, 

 bones, shells and the like, are preserved, 

 and in the case of vertebrates how seldom 

 is even the skeleton completely recovered ! 

 As in plants, the association of the various 

 parts of a single skeleton may require the 

 long continued and laborious efforts of 

 many workers. Extraordinary blunders 

 have sometimes been committed in this 

 work. In the remarkable genus Chalico- 

 therium the skull was at first referred to one 

 mammalian order and the feet to another, 

 and Forsyth-Major's suggestion that they 

 all belonged together was received with in- 

 credulity. Of the even more curious Agri- 

 ochcerus the head was ascribed to one order, 

 the fore-leg to a second and the hind-foot 

 to a third. 



The utterly false notion, which nothing 

 seems able to eradicate, that the paleontolo- 

 gist can readily restore an extinct type from 

 a single bone or tooth, ought to receive its 

 quietus from such examples, though of course 

 it will not. It is equivalent to saying that 

 we have nothing to learn from the fossils, 

 and that all possible types of structure are 

 exemplified in the living world. 



On account of this incompleteness of 



