NOVEMBEB 6, 1896.] 



SCIENCE. 



675 



confirmed by paleontology so far as evi- 

 dence is available, may be extended be- 

 yond the period in which such evidence is 

 to be found. 



And now our last endeavor must be to 

 obtain some conception of the amount of 

 evolution which has taken place within the 

 higher Phyla of the animal kingdom dur- 

 ing the period in which the fossiliferous 

 rocks were deposited. The evidence must 

 necessarily be considered very briefly, and 

 we shall be compelled to omit the Yerte- 

 brata altogether. 



The Phylum Appendiculata is divided by 

 Lankester into three branches, the first con- 

 taining the Rotifera, the second the Chgeto- 

 poda, the third the Arthropoda. Of these 

 the second is the oldest and gave rise to 

 the other two, or at any rate to the Arthro- 

 poda, with which we are alone concerned, 

 inasmuch as the fossil records of the others 

 3;re insufficient. The Arthropoda contain 

 seven classes, divided into two grades, ac- 

 cording to the presence or absence of anten- 

 nae — the Ceratophora, containing the Peri- 

 patoidea, the Myriapoda and the Hexapoda 

 (or insects) ; the Acerata, containing the 

 Crustacea, Arachnida, and two other classes 

 (the Pantopoda and Tardigrada) which we 

 need not consider. The first class of the 

 antenna-bearing group contains the single 

 genus Peripatus — one of the most interest- 

 ing and ancestral of animals, as proved by 

 its structure and development and by its 

 immense geographical range. Ever since 

 the researches of Moseley and Balfour, ex- 

 tended more recently by those of Sedgwick, 

 it has been recognized as one of the most 

 beautiful of the connecting links to be found 

 amongst animals, uniting the antenna-bear- 

 ing Arthropods, of which it is the oldest 

 member, with the Chsetopods. Peripatus is 

 a magnificent example of the far-reaching 

 conclusions of zoology, and of its superiority 

 to paleontology as a guide in unravelling 

 the tangled history of animal evolution. 



Peripatus is alive to-day, and can be studied 

 in all the details of its structure and de- 

 velopment ; it is infinitely more ancestral, 

 and tells of a far more remote past than 

 any fossil Arthropod, although such fossils 

 are well known in all the older of the Palaeo- 

 zoic rocks. And yet Peripatus is not 

 known as a fossil. Peripatus has come 

 down, with but little change, from a time, 

 on a moderate estimate, at least twice as 

 remote as the earliest known Cambrian fos- 

 sil. The agencies which, it is believed, have 

 crushed and heated the Archaean rocks so 

 as to obliterate the traces of life which they 

 contained were powerless to efface this an- 

 cient type, for, although the passing gener- 

 ations may have escaped record, the like- 

 ness of each was stamped on that which 

 succeeded it, and has continued down to 

 the present day. It is, of course, a perfectly 

 trite and obvious conclusion, but not the 

 less one to be wondered at, that the force 

 of heredity should thus far outlast the ebb 

 and flow of terrestrial change throughout 

 the vast period over which the geologist is 

 our guide. 



If, however, the older Palaeozoic rocks 

 tell us nothing of the origin of the antenna- 

 bearing Arthropods, what do they tell us 

 of the history of the Myriapod and Hexapod 

 Classes ? 



The Myriapods are well represented in 

 Palaeozoic strata, two species being found in 

 the Devonian and no less than thirty-two 

 in the Carboniferous. Although placed in 

 an Order (Archipolypoda) separate from 

 those of living Myriapods, these species 

 are by no means primitive and do not sup- 

 ply any information as to the steps by 

 which the Class arose. The imperfection 

 of the record is well seen in the traces of 

 this Class ; for between the Carboniferous 

 rocks and the Oligocene there are no re- 

 mains of undoubted Myriapods. 



We now come to the consideration of in- 

 sects, of which an adequate discussion 



