170 DALY. 



western Pacific or that of the Indian ocean, and, from the proximity 

 of the huge ice-caps of lun-ope and North America, must have been 

 more chilled during the Glacial period than were the other oceans. 

 This conclusion affords a possible explanation of the thorough con- 

 trasts between the reef-coral fauna of the Atlantic and that of the 

 Indo-Pacific province. Hartme^'er says that the species are " niemals 

 identisch," the West Indian species showing a strong excess of Gor- 

 gonidae or horn corals. ^^ The Atlantic and Pacific were connected, 

 across Central America, in the late Tertiary, when, therefore, the reef 

 faunas should have been similar. The closing of this direct passage, 

 during the Miocene or Pliocene, tended to separate the Atlantic reef- 

 coral fauna from that of the greater ocean ; but even then, because of 

 the failure of a marine-temperature barrier south of Africa, the separa- 

 tion may not have been complete. However, since the last Pleisto- 

 cene chilling, the low sea temperature has tended to isolate the relict 

 coral fauna of the Atlantic, whereby it remains quite different from 

 the fauna of the Pacific-Indian basin. Reef-coral larvae cannot now 

 round Cape Horn. Except for a few weeks in the southern summer, 

 the surface temperatures at the Cape of Good Hope are well below 

 20°C. Though it is theoretically possible for coral larvae to drift 

 from parent reefs within the Indian ocean into the Atlantic basin, 

 the chance that they could there settle, mature, and propagate is 

 extremely small; for the shortest path of the drifting larvae would 

 be from Madagascar to the Gulf of Guinea, a distance of about 7,000 

 km. The actual path must necessarily be much longer. One may 

 well doubt that the few larvae which can round the Cape during the 

 southern mid-summer would sur\'ive so long a journey. In any case, 

 the thermal barriers between the Atlantic and Indo-Pacific areas 

 of coral reefs have been nearly perfect for much of post-Glacial time. 

 Special destruction of corals in the Atlantic during the Glacial period, 

 together with the influence of thermal barriers, may, then, explain 

 this faunal contrast. 



On the other hand, the general absence of identical species in the 

 two oceans might be explained by a rapid evolution of types in this 

 admittedly protean group of animals, since the late-Tertiary closing 

 of the Panaman passage. 



The problem of the relation between Pleistocene chilling of the 



19 A. Heilprin, The Geographical and Geological Distribution of Animals. 

 New York, p. 248 (1887);—. Hartmever, Mitt. Geog. Ges. Miinchen, 3, 129 



(1908). 



