ANTARCTIC ROTIFERA 59 



appears therefore to be best adapted to secure success in the struggle for existence 

 under the severe conditions experienced at Cape Royds. 



Dispersal. Most of the Bdelloid Rotifers were found generally distributed 

 among the lakes of the district. Dispersal from one to another is therefore prob- 

 ably easy. The most striking exception is Green Lake, where there are only two 

 of the species. There is little doubt that the qualities of the water are responsible 

 for the limitation in that lake, as there are other lakes close by from which rotifers 

 might be derived. 



Hydatina is only known in Coast Lake. It is the only normally free-swimming 

 rotifer in the region, and very likely its large eggs fall to the bottom in the deeper 

 part of the lake, and are not likely to be in the marginal zone which is exposed by 

 the ablation of the ice. Even so it is to be expected that some eggs would get 

 among the weeds which are thus exposed. 



No rotifers were found in Pony Lake, but the proximity of the penguin rookery 

 renders the water so foul that it would be surprising if there were rotifers in it, 

 always excepting Hydatina, which frequents such situations. 



There are only two probable means by which rotifers can be transferred from one 

 lake to another. One is by the agency of birds, and the other is by means of the 

 wind. The skua gulls are the only birds which frequent the fresh water. They are 

 very fond of bathing, and stand in the shallow parts of the lakes, where the water is 

 a few inches deep and the bottom usually covered with weed and rotifers, and there 

 they splash the water about with great gusto. Fragments of weeds may adhere 

 to their feet or may get on their feathers as the water splashes over them. The 

 skuas may visit several ponds in the course of their flights and thus distribute the 

 rotifers over the countryside. 



At the margins of the lakes there is generally a zone of dried weed, which 

 increases in breadth as the winter advances, as a result of the ablation of the ice 

 surface. This zone varies in colour from brown to dull green. The weed is strongly 

 wrinkled and very light. Pieces of it might easily be torn off by the wind and blown 

 about the country till the next summer, when it might happen to get into another 

 body of water. Fragments of weed were often seen blowing about. In Coast Lake 

 the ablation of the ice exposed the weed on the bottom, which was in small flakes. 

 Showers of these flakes were blown by the wind over the shore and out to sea. 



Dispersal by the wind and conveyance from lake to lake in a small district like 

 Cape lioyds is easily understood. The prevalent strong winds in the region are all 

 from the south, and it is therefore difficult to imagine that the plants and their living 

 freight could be transferred in this way over long distances where there are not 

 intermediate resting-places, except from south to north. It is, however, possible that 

 northerly gales occur at long intervals, which would help to disperse the species in 

 the opposite direction. 



Distribution. Of the distribution of the Rctifera in the Antarctic Region there is 



