390 AUTHITR DENPY. 



Australia and New Zealand respectively is very remarkable. 

 They must have had a common origin, and the question arises, 

 "Did the ancestral form enter Australasia from the north or 

 from the south ? " Either view might be maintained. It may 

 have spread northwards from an Antarctic continent or archi- 

 pelago, as some of the Australasian plants are supposed to 

 have done ; or it may have come from the north at a time when 

 a more or less close connection existed between New Zealand 

 and North-Eastern Australia. Personally I am inclined to 

 favour the latter hypothesis, which seems to be supported by 

 the distribution of Ooperipatus and certain other animals 

 and plants at the present day. It is generally believed that 

 New Zealand has been disconnected from the Australian 

 continent since at least the close of the Cretaceous epoch, and 

 the distribution of Ooperipatus, therefore, indicates a very 

 remote antiquity for the egg-laying habit. In fact, we may 

 believe that the oviparous species have persisted with little 

 modification since the Cretaceous period. It is, of course, just 

 possible that Ooperipatus spread from New Zealand to 

 Australia, or vice versa, across the Tasman Sea in com- 

 paratively recent times, but this appears to me highly im- 

 probable. 



Wherever the ancestral form may have originally come from, 

 it appears not only to have maintained itself successfully in 

 Australasia, but to have given rise to several new species 

 which have lost the primitive oviparous habit ; in Australia 

 P. Leuckartii and P. occidentalis, and in New Zealand 

 P. novse-zealandiaD and P. Suteri may be looked upon as 

 descended from a common oviparous ancestor. 



Thus the distribution of the Australasian species seen)s 

 perfectly consistent with the view that the habit of laying- 

 large and heavily yolked eggs is more primitive than tliat of 

 retaining the young in the uterus throughout the period of 

 their development. This view is also strongly supported by 

 the testimony of Sedgwick and Sclater, derived from the 

 study of the development of viviparous species. 



Sedgwick, dealing with the development of P. capensis. 



