506 LAND ANIMALS 



great annual difference in the distribution of sunlight. The long mid- 

 summer days in the polar regions enable animals to search for food 

 without interruption. Many birds and insects require very little sleep 

 or rest. The domestic fowl requires only three hours, and ants have 

 been observed to work by moonlight. 1 The petrels of South Georgia 

 may be active during the entire 24 hours; ducks are active day and 

 night on Lake Myvatn in Iceland. Bumblebees, unlike other insects 

 in the Arctic, continue to work without regular rest. 2 This amounts to 

 a great increase in the effective working and feeding time, in the short 

 summer. The long day also favors the growth of vegetation. Grass 

 springs up, and many plants are able to bloom and ripen seed in 

 spite of the short season; this is an important factor to the polar ani- 

 mal life. 



Antarctic life. — The Antarctic, with its isolated land mass and high 

 mountains, affords an extreme contrast with the Arctic. The winters 

 are less cold, but the summers less warm than in the Arctic. The low 

 annual temperature in itself does not prevent the development of 

 plant and animal life in Antarctica, if only the distribution of heat is 

 such that the summers are sufficiently warm. On Seymour Island, for 

 example, at 64° S. latitude, about the latitude of Drontheim in Nor- 

 way, the warmest month (January) has a mean temperature of — 0.9°, 

 and that of the three summer months is — 2.15°. In the Antarctic the 

 summer temperature remains almost constantly below the minimum 

 for the development of higher plants. There are consequently only two 

 flowering plants, a grass and a Colobanthus, on the continent of 

 Antarctica and its near-by islands, and only a few species of mosses 

 and algae maintain a precarious existence, while some 400 species 

 of flowering plants grow north of the Arctic Circle, 3 and even on 

 west Greenland, 600 miles north of the Arctic Circle, Ekblaw re- 

 ported 120 species of flowering plants including chickweed and dande- 

 lion. The subantarctic South Orkney Islands (61° S. latitude) have no 

 flowering plants, while a hundred species bloom in Spitzbergen (79° 

 N. latitude) in summer. Land vertebrates are accordingly absent in 

 Antarctica ; the birds and mammals are wholly dependent on the wealth 

 of life in the sea. Invertebrate life in the Antarctic is also surprisingly 

 poor and there is almost no land fauna away from the penguin rook- 

 eries where one may find minute springtails, a wingless chironomid 

 fly, tardigrades, mites, a few rotifers, and two or three protozoans. 

 They are active for but a few days at most during the year and can 

 exist for months, perhaps for years, in a frozen state. 3 The only widely 

 distributed species of antarctic insects are parasites on seals. 4 



