70 ETIKNNK GEOFFROY SAINT-HILAIRE 



German transcendental thought, and was developed later by 

 his disciple E. Serres, the law that the higher animals repeat 

 during their development the main features of the adult 

 organisation of animals lower in the scale. Thus he compared 

 fish as regards certain parts of their structure with the foetus 

 of mammals. He compared also Articulates with embryonic 

 Vertebrates in respect of their vertebrae, for in the higher 

 Vertebrates the body of the vertebra is tubular at an early 

 stage of development, and in .Articulates the body of the 

 vertebra remains tubular permanently (supra, p. 61). As 

 regards their vertebrae, " insects occupy a place in the series 

 of the ages and developments of the vertebrate animals, that 

 is to say, they realise one of the states of their embryo, as 

 fishes do one of the states of their foetal condition." 1 



This idea was destined to exercise a great influence upon 

 the development of morphology. A further development of 

 the thought is that certain abnormalities in the higher 

 animals, resulting from arrest of development, represent 

 states of organisation which are permanent in the lower 

 animals. 2 



So far we have considered Geoffroy's theories in their 

 application to the facts. We go on to discuss the theories 

 themselves, and the general conception of living things which 

 underlies them. 



The principle of unity of plan and composition is the 

 keynote of Geoffroy's work. It states that the same 

 materials of organisation are to be found in all animals, and 

 that these materials stand always in the same general spatial 

 relations to one another. The " materials of organisation " 

 are not necessarily organs in the physiological sense, and 

 indeed the principle of the unity of plan cannot be upheld if 

 the unity has reference to organs only. This became clear 

 to Geoffroy, especially in his later years. In 1835 he wrote, 

 speaking of the principle of the unit} 7 of plan, " I have, more- 

 over, regenerated this principle, and obtained for it univer- 

 sality of application, by showing that it is not always the 

 organs as a whole, but merely the materials composing each 



1 Mt'in. Mns. d' Hist. ;/<//., ix., ]>. 101, 1822. 



-' dntrs dc Phistoirc natitrcllc dcs Altuninifcrcs^ i., Le^on 3, p. 13, 

 1829. 



