02 ETIENNE GEOFFROV SAINT-HILAIRE 



by the way, in the same transverse plane as the body of 

 the vertebra). Every vertebra, he considers, contains these 

 nine pieces the cycleal (or body), the two perials (e', e") 

 and the two epials (a', a") above, the two paraals (o', o") and 

 the two cataals (u', u") below. The epials and the cataals 

 are in reality paired bones which in fish mount one on top 

 of the other to support the median fins. In the cranial 

 region the skull is formed of modified vertebrae the epials 

 and perials open out so as to form the walls and roof of the 

 brain ; in the thoracic region the paraals and cataals reach 

 their maximum of development and perform the same service 

 for the thoracic organs, the paraals becoming vertebral, and 

 the cataals sternal, ribs. 



We have seen that in Arthropods the body of the 

 vertebra (cycleal) forms the open ring of the segment, which 

 lies immediately under the skin, the vertebral tube coinciding 

 with the epidermal tube. The homologues of the other 

 eight pieces of the vertebra must accordingly be sought in 

 the external appendages. At first sight there seems here a 

 contradiction of the principle of connections, for the 

 appendages in Arthropods are lateral, whereas the paired 

 bones of the vertebra are dorsal and ventral. But there is 

 in reality no contradiction, for " what our law of connections 

 absolutely requires is that all organs, \vhether internal or 

 external, should stand to one another in the same relations ; 

 but it is all one whether the box (coffrc) that encloses 

 them lies with this or that side on the ground. What 

 similarities in the organisation of man and the digitate 

 mammals, and yet what differences between their attitudes 

 when standing ! The same holds true as regards the 

 normal attitudes of the pleuronectids and the other fishes " 



The exact way in which Geoffrey homologised the parts 

 of the appendages in Arthropods with the paired pieces of 

 the typical vertebra is best shown by the reproduction of his 

 figure of an abdominal segment of the lobster (Fig. 3), in 

 which the parts homologous with those represented in the 

 figure of the typical vertebra (Fig. 2) are indicated by 

 the same letters. The ingenuity of the comparison is 

 astonishing. 



