42 CHAPTERS ON EVOLUTION. 



to be we discover the great truth that both animals are built up on 

 the same fundamental type. In a word, the ideal diagram (Fig. 4) 

 we have constructed of the lobster's body will serve equally well to 

 indicate the broad features of butterfly-structure. And further, as 

 all crustaceans can be shown to possess bodies modelled on the 

 lobster type, so all insects numbering many thousands of species 



FIG. 4. DIAGRAM OF AN ANNULOSE ANIMAL. 



i. Diagrammatic longitudinal section of Annulose animal : a, blood or haemal 

 system ; b, digestive system : c, neural or nervous system. 2. Nervous 

 system of Annulose animal, viewed from above, and showing the double 

 ventral nervous chain. 3. Transverse section of Annulose animal : a, blood 

 system; b, digestive system; c, nervous system; dd, gills or breathing 

 organs ; e e sa&ff, "oars" or locomotive organs. 



may, without exception, be referred to the butterfly type. From 

 which declarations a third may naturally be drawn, namely, that the 

 bodies of all insects and all crustaceans are built up on one and the 

 same fundamental plan. Nor is this all. The diagram (Fig. 3) which, 

 as we have seen, conveys to our mind the essential features in the 

 anatomy of a lobster and a butterfly, and which, through these 

 animals, presents us with a general idea of every insect and every 

 crustacean, can be shown to possess a more extended application 

 still. Every spider, scorpion, and mite agrees with the lobster and 

 insect in its essential structure ; and every centipede and millipede 

 likewise has its heart above, its nervous system below, and its diges- 

 tive system in the middle of its body; whilst if we, lastly, examine the 

 worms themselves, we shall find that our diagram still serves to show 

 the main details of the structure of that extensive class. In this way, 

 therefore, the language of the zoologist becomes clear when he states 

 that all of the foregoing animals constitute " a type of animals." The 

 type in question is, in fact, Cuvier's Articulata, or, as it is rendered in 

 modern zoology, that of the Annulosa. And there remains yet one 

 important addition to the zoological statement, namely, that no other 

 animals, save the Annulosa or Articulates, exhibit the arrangement of 

 parts just noted.. The heart above and the nervous system below 

 (Fig. 4, i) are characters as distinctive of these animals as is the 



