THE ARTHROPOD AND THE VERTEBRATE 63 



The comparison of the Arthropod with the Vertebrate is 

 extended also to the internal organs. The internal organs 

 of the Arthropod are shown to stand in the same order to one 

 another as in the Vertebrate, only the organs are inverted. 

 Thus the nervous system is dorsal in the Vertebrate, ventral 

 in the Arthropod. Turn the Arthropod on its back and the 

 relative positions of the systems of organs are the same as in 

 the Vertebrate. The relation of the organs to the external tube 

 is of course different in Arthro- 

 pods and Vertebrates, but this 

 is no contradiction of the prin- 

 ciple of connections. " Such a 

 tube, although it is the organs 

 essential to life that it 

 contains, can yet behave in 

 different ways with regard to 

 the mass of these organs : 

 the principle of connections 

 demands only that all the 

 organs maintain with one 

 another fixed and definite re- 

 lations ; but the principle 

 would be in no way invali- 

 dated if the whole mass had 

 rotated inside the tube" (p. 

 112). 



Geoffrey pushed the anal- 

 ogy between Arthropods and 

 Vertebrates very far, for he 

 asserted that every piece in 

 the skeleton of an insect was 

 homologous ' with some bone 

 in Vertebrates, that it stood 



FlG. 3. Abdominal Segment of the 

 Lobster. (After Geoffrey.) 



always in its proper place, and remained faithful to at 

 least one of its connections. 1 It does not appear that he 

 attempted to prove in detail this very big assumption, but 

 the beginnings of a detailed comparison are found in the 

 paper of 1820, Sur F organisation dcs insectcs. Six segments 

 are distinguished in an insect the head, the three divisions 

 1 Sur P organisation des insec/es, p. 459. 



