LIFE IN PRIMARY PERIOD 235 



Whenever the limbs of an animal are missing or are not used for 

 locomotion, the body elongates thus and the segments multiply. 

 This proposition is as true of Arthropods and Worms as of 

 Vertebrates in which the number of body segments is indicated 

 by that of the intercalated vertebras. Like other biological 

 propositions, it is capable of being interpreted in two contra- 

 dictory ways, both of which may be correct under different 

 circumstances : Firstly, the body if it elongates sufficiently for 

 undulatory movements to satisfy all the needs of locomotion, ren- 

 ders the limbs useless, and they become atrophied through lack 

 of use ; secondly, if the limbs become too short to lean on the 

 ground, or give the body sufficient speed, the body itself will 

 take an active part in locomotion. The increase in its 

 activity means a greater intensity in the phenomena of 

 nutrition, which by tachygenesis may already manifest itself 

 during the period of multiplication of the body segments. 

 The number of these segments then increases, and the body 

 itself becomes more and more capable of providing for the 

 animal's peregrinations. The first interpretation would seem 

 to fit the case of primitive animal organisms, in which an 

 indefinite multiplication of the body parts is a sign of their 

 reciprocal independence and a mark of inferiority. That can 

 be admitted for the Myriapods, such as Geophilus, with 

 their elongated bodies, and for errant Annelids such as 

 Myrianidae, Phyllodocidae, Nereidae, Eunicidae or even Nais, etc. 

 The second interpretation, on the other hand, especially 

 fits the Vertebrates, in whom the number of body segments 

 early became limited and in whom locomotion was accomplished 

 very early by the aid of limbs whose original insufficiency 

 we cannot admit. The aquatic Vertebrates, in which the 

 undulatory movements of the body clearly play a pre- 

 ponderating part in locomotion, have especially good reasons 

 for neglecting to use their limbs when moving, and it has been 

 proved precisely in the case of existing species which live 

 under special conditions that this atrophy of the limbs 

 coincides with a multiplication of the body segments. This is 

 clear in the case of the Proteidae of the Adelsberg cave, 

 in Carniola, in which the fore-limbs have only three digits 

 and the hind-legs two. They preserve their gills all 

 their life and, by tachygenesis, are born with the four legs of 

 the adult. 1 This is shown even better in the lacertine 



1 Marie de Chauvin, Zeitschrift /. wissenschaftliche Zoologie, Bd. xxxviii, 

 1883, p. 671, and Nature, vol. be, p. 389. 



