M. A. Milne-Echvanls on the Group of the Mole-Rats. 157 



of niaxillipedes of the male, are developed, and the limbs, 

 Avhieli are then no longer ealled into aetion, are gradually 

 ahorted and disa})pear. The male, on the other hand, will not 

 be subject to such a transformation 5 for '' his task is always 

 that of vigorous sexual activity — above all, to seek the female for 

 the purpose of copulation " (Claus, '■ Freilebende Coi)epoden,' 

 p. 7) ; he consequently never acquires the characters established 

 for the family and genus. It follows, however, from the above 

 that both sexes of the Lerniea here in question show a grade 

 of development such as we find again only among the Diche- 

 lestiinffi, and such as the ChondracantJue and Lerna'Ojwdce do 

 not attain, which evidently may be of some importance in 

 connexion with the systematic position of the Lerncece. 



XXIII. — Observations on the Group of the Mole-Bats. 

 By M. A. Milne-Edwards*. 



The conditio7is of existence imder which animals are placed 

 generally coincide with certain peculiarities of organization, 

 and tend to modify the external form of these creatures to tit 

 it for the necessities to which they are subjected. Thus we 

 see, in nearly all the orders of Mammalia, natatory species side 

 by side with terrestrial species, and among the latter there are 

 often some which lead a subterranean life. These biological 

 conditions betray themselves outwardly by organic modifica- 

 tions, which, whilst mutually presenting a great similarity, are 

 realized by animals of very different types. Analogies which 

 depend upon the modification of the animal machine to a 

 special mode of existence may be observed not only between 

 species belonging to different orders, but also between species 

 of the same order and of different families. Frequently an 

 exaggerated importance has been ascribed to them, and certain 

 peculiarities have been taken for dominant characters which, 

 without having any influence upon the organic plan of the ani- 

 mal, had merely modified its external appearance. The species 

 which form the subject of this memoir are afresh proof of this. 

 ]\I()St zoologists have combined in a single group those 

 Rodentia which lead a subterranean life, which dig deep 

 galleries by means of their claws, and feed iq)on the roots and 

 bulbs of plants. In their general aspect these animals have 

 something that reminds one of the ^loles : their body is thick, 

 more or less cylindrico-conical, and borne u])on short and 

 robust limbs ; alid their eyes are often scarcely open. On 



* Translated from the 'Comptes Rendus,' Aufrust 17, 18(38, tome Lxvii. 

 pp. 4 '.8-441 . 



