126 HABITUDES AND ATTITUDES 



The Onychophora furnish instructive gradations 

 from placentation, at one extreme, to oviposition 

 at the other, the sizes of the eggs increasing pari 

 passu from minimal to maximal dimensions. The 

 species show a peculiar correlation between their 

 geographical distribution and their morphological 

 differentiation ; T and to some extent, though not 

 entirely, the modes of development vary with 

 the distribution. The placental condition of the 

 small - egged South American species is highly 

 specialised ; the oviparous habit of some Austra- 

 lasian species 2 is, to my mind, clearly secondary. 

 As for the species themselves, one form is not 

 appreciably more primitive than another. 



In this group, therefore, the two extreme 

 methods of nutrition of the embryo are equally 

 cenogenetic. There still remain three inter- 

 mediate states of the embryo, namely, the tropho- 

 blastic development of the small - egged New 

 Britain species, and also of a South African 

 species ; the normal or direct development of 

 the Cape species ; and the yolky or meroblastic 

 development of some Australian and Malayan 

 species. 



Just as among aquatic organisms which dis- 

 charge their spawn freely into the water, a 



1 Cf. Adam Sedgwick, "The Distribution and Classification of 



the Onychophora," Quart. Journ. Micr. Sc, vol. lii., 1908, pp. 

 379-406. 



2 Cf. A. Dendy, " On the Oviparous Species of Onychophora," 

 Quart. Journ. Micr. Sc, vol. xlv., 1902, pp. 363-414. 



