84 M. A. Giard on the Position of Sagitta, and on 



type of the monkey with hands and with a prehensile tail ap- 

 pears first of all in the chameleon — a reptile which does not creep 

 but climbs, and twists its tail round the branch that bears it. 

 This type reappears among the marsupials in the phalangers 

 and opossums, among the rodents in the couendous {Syne- 

 theres), and among the plantigrade carnivores in the kinkajou 

 (Cercoleptes) , to become multiplied, diversified, and terminated 

 in the prehensile-tailed monkeys of South America, such as 

 the sapajous, howling monkeys, and spider monkeys. The 

 flying dragon, among reptiles, is the first appearance of an 

 animal which sustains itself in the air by means of a membrane 

 stretched upon the sides of the trunk. The flying phalanger 

 or Petaarista among marsupials, the flying squirrel among the 

 rodents, and, lastly, the Galeojnthecus or flying lemur are re- 

 petitions of the same morphological type from the reptiles up 

 to the primates In the gradual evolution of living- 

 creatures, notwithstanding profound differences of organization, 

 the same media and the same needs have induced the develop- 

 ment of the same forms, which heredity has fixed and main- 

 tained by the reproduction of the species." 



It will be seen that the learned Professor takes especially 

 as examples organic arrangements relating to vital peculia- 

 rities of secondary rank. Thus we may say that some 

 animals, such as the chameleon, the opossum, &c, present the 

 same etiological type, rather than the same morphological type 

 in the true sense of the word. It is the same with other 

 animals with still more superficial resemblances due to 

 direct mimetism, and not to parallelism of vital conditions*. 

 The action of surrounding media is of course exerted from the 

 exterior towards the interior, and does not succeed in modify- 

 ing the morphological type in creatures which are already 

 strongly differentiated until after a very long time, and only 

 with the aid of very imperious physiological necessities. As a 

 matter of course, however, these physiological necessities are 

 powerless of themselves to induce the convergence of types ; 

 and whilst we render all justice to our immortal Lamarck, 

 we must not lose sight of the part played by natural selection 

 in the preservation of the forms which are best adapted to a 

 definite ensemble of external conditions. 



One of the most energetic factors of this convergence is 

 certainly, as has already been said, parasitism, and especially 

 parasitism in its most absolute form — that is to say, that which 



* See, for more details upon the resemblances due to mimetism, my 

 ' Recherches sur les Synascidies,' pp. 58 et seqq. The interesting inves- 

 tigations of Wallace and of some other zoologists are far from having 

 exhausted this subject, which for many reasons deserves to be investi- 

 gated afresh. 



