THE FLY. 37 



of our subject, that we should inquire what principle 

 has of late guided zoologists in their systematic ar- 

 rangement of these forms ; and it will then also be- 

 come obvious what reason has induced us to couple 

 together in this little treatise two such apparently 

 opposite creatures as the Worm and the House-Fly, 

 employing the first as an introduction to the more 

 complicated structure of the second*. 



Those who have acquired at all a scientific know- 

 ledge of zoology, are well aware that each great divi- 

 sion of the Animal Kingdon exhibits a progressive 

 development in the organization of the various groups 

 that it contains ; and also, that in following the life- 

 history of a single individual in that section, a re- 

 markable analogy is apparent between the various 

 stages of development through which it passes, and 

 those to which we have just referred as existing in 



* In glancing over a Synopsis of the Hunterian Lectures on 

 tlie anatomy and classification of the Invertebrate animals, 

 delivered last year by Professor George Busk, F.E.S., at the 

 Koyal College of Surgeons, we find the relation between the 

 Worm and the Fly denoted in a striking manner by the classi- 

 fication which that physiologist has adopted. 



Under the title of "Annulosa," or annulated animals, he in- 

 cludes every creatiire possessing a body composed of rings or 

 segments, and amongst the subdivisions of that great class we 

 find that he unites the Annelides (of which the Earthworm is 

 the typical representative) to the Insecta, whereof the Fly is 

 one of the characteristic forms, by the Myriapoda (Centipedes), 

 which partake of the nature of both groups. 



We have seen no classification that confirms so clearly as 

 this, the idea which induced us to couple the Worm and the 

 Fly in one treatise. — (See pag'e 10, Letter II. " Natantia.") 



c3 



