130 CRITIQUES AND ADDRESSES. [vi. 



Jukes, has suggested, give us indications of the manner 

 in which some of the most puzzling facts connected 

 with the distribution of animals have been brought 

 about. For example, Australia and New Guinea are 

 separated by Torres Straits, a broad belt of sea 100 or 

 120 miles wide. Nevertheless, there is in many respects 

 a curious resemblance between the land animals which 

 inhabit New Guinea and the land animals which 

 inhabit Australia. But, at the same time, the marine 

 shell-fish which are found in the shallow waters of 

 the shores of New Guinea, are quite different from 

 those which are met with upon the coasts of Australia. 

 Now, the eastern end of Torres Straits is full of atolls, 

 which, in fact, form the northern termination of the 

 Great Barrier Eeef which skirts the eastern coast of 

 Australia. It follows, therefore, that the eastern end 

 of Torres Straits is an area of depression, and it is 

 very possible, and on many grounds highly probable, 

 that, in former times, Australia and New Guinea were 

 directly connected together, and that Torres Straits did 

 not exist. If this were the case, the existence of casso- 

 waries and of marsupial quadrupeds, both in New Guinea 

 and in Australia, becomes intelligible; while the differ- 

 ence between the littoral molluscs of the north and the 

 south shores of Torres Straits is readily explained by 

 the great probability that, when the depression in 

 question took place, and what was, at first, an arm of 

 the sea became converted into a strait separating Aus- 

 tralia from New Guinea, the northern shore of this new 

 sea became tenanted with marine animals from the north, 

 while the southern shore was peopled by immigrants 

 from the already existing marine Australian fauna. 



Inasmuch as the growth of the reef depends upon 

 that of successive generations of coral polypes, and 

 as each generation takes a certain time to grow to its 



