10 TIIK BEGINNINGSOF COMPARATIVE ANATOMY 



elsewhere that they are only analogous structures (ii., 

 81 653 b ). I' 1 the same connection he describes also the 

 supporting tissues of Invertebrates the hard exoskeleton 

 of Crustacea and Insects, the shell of Testacea, the " bone " of 

 Sepia (ii., 8, 654*). Aristotle took much more interest in 

 analogies, in organs of similar function, than in homologies. 

 He did recognise the existence of homologies, but rather 

 nidlgre Ini, because the facts forced it upon him. 



His only excursion into the realm of " transcendental 

 anatomy" is his comparison of a Cephalopod to a doubled-up 

 Vertebrate whose legs have become adherent to its head, 

 whose alimentary canal has doubled upon itself in such 

 a way as to bring the anus near the mouth (De Partibns, iv., 

 9, 684 b ). It is clear, however, that Aristotle did not seek to 

 establish by this comparison any true homologies of parts, 

 but merely analogies, thus avoiding the error into which 

 Meyranx and Laurencet fell more than two thousand years 

 later in their paper communicated to the Academic des 

 Sciences, which formed the starting-point of the famous 

 controversy between Cuvier and E. Geoffroy St Hilaire 

 (see Chap. V., below). 



Moreover, Aristotle did not so much compare a Cephal- 

 opod with a doubled-up Vertebrate as contrast Cephalopods 

 (and also Testacea) with all other animals. Other animals 

 have their organs in a straight line ; Cephalopods and 

 Testacea alone show this peculiar doubling up of the 

 body. 



(4) Aristotle was much struck with certain facts of 

 correlation, of the interdependence of two organs which 

 are not apparently in functional dependence on one another. 

 Such correlation may be positive or negative ; the presence 

 of one organ may either entail the presence of the other, or 

 it may entail its absence. Aristotle has various ways of 

 explaining facts of correlation. He observed that no animal 

 has both tusks and horns, but this fact could easily be 

 explained on the principle that Nature never makes anything 

 superfluous or in vain. If an animal is protected by the 

 possession of tusks it docs not require horns, and vice 

 . The correlation of a multiple stomach with deficient 



