24 FROM FISH TO PHILOSOPHER 



brates— comprise only 25,000 species distributed among 

 the fishes, Amphibia, reptiles, birds, and mammals— 

 with man, of course, as a single mammahan species men- 

 tioned modestly at the end. We are concerned here only 

 with the vertebrates, because man is a vertebrate. That 

 the lowest vertebrates were themselves evolved out of 

 some invertebrate race is accepted by everyone; but 

 what race, no one knows. The history of this area of 

 biological speculation appears as an introductory chap- 

 ter in almost every textbook of vertebrate biology, and 

 serves on the whole only to confuse the student and 

 reduce to doubt his faith in the order of nature. Geoffrey 

 Saint-Hilaire (1818) saw in the vertebrate merely a 

 much-modified insect turned over on its back. Since his 

 time, theory has succeeded theory: Hubrecht (1887) 

 would have derived the vertebrates from the nemertean 

 worms; Bateson (1884, 1885) from the acorn worms; 

 Kovalevsky (1866) and Brooks (1893) from the tuni- 

 cates; and Semper (1875), Minot (1897), Marshall 

 (1879), Balfour (1881), Gegenbaur (1887), Eisig 

 (1887), and Delsman (1913)— all great names in biol- 

 ogy—tried by devious tricks of evolutionary legerdemain 

 to obtain them from one or another type of anneKd 

 worm; Masterman (1898) from the jellyfish; while Gas- 

 kell (1896-1908) and Patten (1884-1912) confidently 

 saw the prototype in the ancient arachnids, of which 

 Limulus is a lonely survivor— thus returning the circle of 

 speculation almost but not quite to Saint-Hilaire's in- 

 verted insects, though with httle more cogency. Gar- 

 stang (1894) was the first to look for the ancestors of 

 the vertebrates in the larval rather than the adult state 

 of some invertebrate, and to point to the larval echino- 

 derms (starfish, sea urchins, sea cucumbers, and such) 

 as a likely source; and Torsten Gisl^n (1930) and W. K. 

 Gregory (1935) explored the larval echinoderm theory 

 with encouraging results. The evidence is not to be found 

 in the fossil record but rather in the comparative anat- 



