358 ANIMAL BIOLOGY 



ing each middle ear with the pharynx. Gill arches, which func- 

 tion as supports for the gills in the aquatic Vertebrates, persist 

 in highly modified form as skeletal structures associated with 

 the tongue and entrance to the lungs (larynx) in terrestrial 

 forms. Finally, in this connection the reader will recall the trans- 

 formations of the blood vessels in the Vertebrates which occur 

 with the substitution of lungs for gills, and also the variations 

 and interrelationships of the excretory and reproductive systems 



in the ascending series of Ver- 

 tebrate classes. (Figs. 121, 

 122, 127, 129, 148, 231.) 



One may, of course, con- 

 clude from all these facts that 

 the various species of verte- 

 brates have each been inde- 

 F u IG V 231 ; ~ He ? d of a f R at tlesna ke, pendently created according to 



with the skin and part ot the muscles r * 



removed. The long oval mass in the the same preconceived plan — 

 upper jaw which is connected by a duct and likewise all the great num- 

 with the curved tooth, the fang is the bersof orders families, genera, 

 poison gland, {r rom Smallwood.) . * _ 



species, etc., ot each ol the live 



classes that these forms represent. Or one may conclude that all 

 have arisen by descent with change from a primitive Vertebrate 

 organism which possessed the fundamental similarities exhibited 

 from Fish to Man. The latter is the conclusion accepted by biolo- 

 gists to-day. 



3. Paleontology 



Huxley once said that if zoologists and embryologists had not 

 put forward the theory of evolution, it would have been necessary 

 for paleontologists to invent it. What then are the main facts 

 offered by paleontology, the study of the fossil remains of ex- 

 tinct animals and plants? 



In the first place it must be made clear that geologists are able 

 to determine, with remarkable accuracy in most cases, the se- 

 quence in time, or chronological succession, of the rock strata 

 composing the Earth's surface. The main outline of this scheme 

 of geological chronology was understood long before the evolution 

 of organisms was a crucial question ; so that we may consider the 

 evidence which it affords of the chronological succession of the 

 fossil remains exhibited by the various strata, as impartial testi- 



