252 M. Edmond Perrier on (he 



XXIX. — The Origin of the Vertebrates. 

 By Edmond Perrier*. 



Since the researches of Kowalevsky (I860) the Vertebrates 

 have been successively derived by authors from indeterminate 

 animals (Scolecida), which were considered to have given 

 rise at the same time to the Tunicates (Hreckel, 1866) ; from 

 the Annelid Worms (Semper, Balfour, 1874; Dohrn, 1875; 

 E. Perrier, 1881 ; Leydwick Minot, 1897) ; from the primary 

 Merostomata (Albert Gaudry, 1883) ; from Balanoglossus 

 (Bateson, 1884) ; from the Nemertines (Hubrecht, 1887) ; 

 from the Arachnids (Patten, 1891) ; from the Crustaceans 

 (Gaskell, 1891) ; from an animal allied to the Appendicu- 

 laridae (Brooks, 1893; Willey, 1894). 



Differences of opinion such as these evidently imply either 

 that the principles of zoology are still badly defined, or else 

 that they are too frequently lost sight of, or else again that 

 sufficient attention has not been paid to determining the 

 nature of the characters of Vertebrates, the explanation of 

 which had to be demanded from ancestral forms. We hope 

 to show in the present paper that a rigorous application of 

 undisputed principles leads to a unique solution of the 

 problem, and that this solution is in every respect satisfactory. 



The following essential characters are exhibited by every 

 Vertebrate : — 



(1) The body is bilaterally symmetrical and metamerically 

 segmented throughout its entire length ; (2) an important 

 extent of its external or internal surfaces, especially those 

 devoted to the respiratory function, is clothed with vibratile 

 cilia ; (3) during the embryonic period, at the very least, the 

 anterior region of the alimentary canal always communicates 

 with the exterior by means of lateral clefts ; (4) the circu- 

 latory apparatus is closed, and exhibits a heart situated below 

 the alimentary canal ; (5) the secretory apparatus is consti- 

 tuted by a system of ducts which are repeated, in the embryo, 

 throughout the whole length of the body, and provide the genital 

 apparatus with its excretory ducts ; (6) above the digestive 

 tract there extends, in the embryo, a solid cord of cells, the 

 voiochord, around which are formed the vertebrae of the adult 

 animal; (7) above thenotochord lies the central nervous system, 

 all on the same side of the alimentary canal, deprived of an 

 oesophageal ring, and exhibiting a considerable bulk ; (8) with 



* Translated by E. E. Austen from the ' Comptes Rendus,' t. exxri. 

 no. 21 (May 23, 18P«), pp. 1479-4486. 



