DISTRIBUTE INSECT VARIETY. 257 



the hammer-bone of the ear. Indej^endent of the season of 

 adolescence, man in the fetal state has been said to pass through 

 the successive forms of fish, reptile, and mammal ; and other 

 organised beings prolong such season of progression into a period 

 subsequent to exclusion, the tadpole relinquishing its pisciform 

 branchiae and tail, and becoming an atmospheric-breathing reptile ; 

 and lower still in the scale we may instance our vermiform insect 

 larva or caterpillar, who sometimes similarly leaves an aqueous 

 life, and by casting successive coverings evolves a winged bird- 

 like form. The parts of plants arise in like fashion, and 

 generally organic species spring with common features and pass 

 through the stages of those inferior in rank previous to assuming 

 the perfect form. The animal kingdom, according to Professor 

 Haeckel, thus indicates divisioii into two classes : those in which 

 there is no internal body-cavity — the Protozoa — and those in 

 which such cavity exists — the Metazoa. From the latter appear 

 evolved on the one hand Echinodermata and Coelenterata, and on 

 the other Vermes ; from which latter, again, all the other grovips 

 of both invertebrates and vertebrates may have arisen."^ 



Lastly, we have the distribution theories lately propounded 

 in this country by Messrs. Sclater, Wallace,t Bates, and others. 

 These, in their wider acceptation, seek characteristic groups 

 presented by the life aspect on the globe^s surface, as confined 

 to certain natural regions or centres of distribution. Consider in 

 what measure a predominance of forms in each locality, as that 

 of the Edentata in South America, or Marsupialia in Australia, 

 may be due to the isolation of oceans, seas, deserts, and mountain 

 chains, whose comparative chronology is known to the geologist, 

 and which modify climatic dispersion; and also examine what 

 claims eccentric species like the Marsupialia of South America 

 have to be treated as remnants of past geological distributions. 

 And, secondly, to determine the laws active in modifying existing 



* Abridged from Prof. Allen Thomson's address, "The Development of the 

 Forms of Animal Life," Brit. Assoc, 47th meeting. In respect to insects, 

 German anatomists have found that the embryos of Mantis, Water Beetles, 

 Bees, &c., have an extra pair of legs that are never perfected ; thus indicating 

 the descent of these insects from a form with eight legs. See Dr. Vitis Graber. 

 " Die Insekten." 



t A. E. Wallace, " Distribution of Animals," and other works and scientific 

 papers. 



R 



