290 THE ZOOLOGIST. 



between the faunas and floras of high northern and high southern 

 latitudes, as shown in the arctic and antarctic marine faunas 

 and floras, is disposed to consider or invoke the deadly effects of 

 a very ancient chilling influence. " In order to give a rational 

 explanation of these remarkable facts in the distribution of 

 marine organisms at the present time, as well as of the presence 

 of tropical fossils in Palaeozoic and even later geological strata 

 within the polar areas, it seems necessary to assume that at one 

 time there was a very different distribution of heat and light 

 over the surface of the globe than what obtains at the present 

 time. A uniform high temperature all over the surface of the 

 globe in the early stages of the earth's history is required to 

 explain these phenomena. In later Mesozoic times a gradual 

 cooling at the poles appears to have set in, and slowly brought 

 about the destruction of a large number of the shore and shallow 

 water animals, especially those which secreted large quantities of 

 carbonate of lime, or were provided with pelagic or free-swimming 

 larvae. This weeding-out of numerous species in the polar areas, 

 from a fauna which must have much resembled the coral-reef 

 fauna of the present time, accounts for the relatively small 

 number of species which we now find in polar waters, and, 

 through lessened competition, for the relatively large number of 

 individuals belonging to some of these species. In still later 

 times, when polar lands became covered with ice and snow, and 

 when glaciers descended at almost all points into the ocean, 

 shallow water organisms appear to have taken refuge in the deep 

 sea, and a migration of polar animals towards the equator was 

 initiated over the floor of the ocean."* 



Although the shorter summer and the longer winter must 

 have undermined the constitution and eventually have destroyed 

 many delicate forms of life, t some, like the Myriapoda, can with- 

 stand great alterations of climate. Mr. Sinclair, in the island 

 of Cyprus, found identical species of Scolopendra and Lithobius 



* ' Coinpte-Bendu,' 3rd Internat. Congr. Zool. Leyden, pp. 109-10. 



f Sir Eobert Ball has argued that the shorter summer and the longer 

 winter is the cause of the ice age, and not, as is so often thought, a less supply 

 of heat from the sun. According to this authority, and worked on mathe- 

 matical calculation which admits " of no dispute," of the total amount of 

 heat received from the sun on a hemisphere of the earth in the course of a 

 year, 63 per cent, is received during the summer, and 37 per cent, during the 

 winter (' The Cause of an Ice Age,' p. 90). 



