PERIPATUS 125 



example, that the egg - laying habit of the 

 Australian monotremes is due to early regression 

 or descent with simplification in a primitive type, 

 while the lecithality of their eggs is not a palin- 

 genetic or high ancestral quality, but adaptive 

 or cenogenetic. 1 The abundance and scarcity 

 of yolk may be alike primitive and secondary 

 features within certain defined limits, in a manner 

 analogous with the plurality and duality of teats 

 in mammals. 2 



It is not only among mammals that we find 

 large eggs associated with oviparity and small 

 eggs with viviparity and placentation ; and not 

 only among marine organisms do we find large 

 eggs associated with direct development and 

 small eggs with indirect development. 



Peripatus is a soft-bodied, cryptozoic animal, 

 living in the tropics under logs and leaves, 

 whose body has the consistency of a caterpillar, 

 and whose feet are numerous like those of a 

 centipede but not jointed. It is known by no 

 other name except that of its own division of 

 the Appendiculata, namely, the Onychophora. 

 The class name Prototracheata was applied by 

 Moseley to this group, but since that time it 

 has been recognised that tracheate animals do 

 not form a homogeneous series, as will be ex- 

 plained more fully below. 



1 This is Professor Hubrecht's view (I.e., 1908). 



2 Cf. A. Willey, " The Lacteal Tract of Lori's gracilis? Spolia 

 Zeylanica, vol. iii., 1905 (1906), pp. 160-162 and figure. 



