ANTARCTIC ROTIFERA 43 



the young are obviously of very different ages, one being fully developed while another 

 shows no detail at all. The yolk mass contains eight nuclei. 



The spurs vary greatly in size, generally most closely resembling those of P. acuti- 

 cornis (25). The interspace is relatively broader. Occasionally they are very long 

 and apparently two-jointed. The last foot-joint is long. The ventral toes are very 

 large, and the dorsal ones very small. 



The vibratile tags are short, and broadly spindle-shaped. Three pairs have been 

 seen. 



Habitat. In lakes and ponds at Cape Royds, Cape Barne, and at the Stranded 

 Moraines on the west side of McMurdo Sound. It was absent from the very saline 

 Green Lake, but was in nearly all the other waters examined. It was much the most 

 abundant species in the district. Its abundance in Coast Lake and in the lake at 

 the Stranded Moraines was remarkable. In winter it was got by digging out ice 

 containing plants from the lakes. As soon as these were thawed the rotifers were 

 found active in great plenty. In summer blood-red patches began to form on the 

 stones at the margin of Coast Lake. These attained to a diameter of an inch. 

 Similar patches were on the plants, but these were more difficult to detect owing to 

 the orano-e-red colour of the plants. In the lake at the Stranded Moraines, Priestley 

 reports that the patches reached to six or eight inches in diameter, and were of 

 appreciable thickness. These patches were formed solely of P. gregaria, which were 

 fixed side by side, as close as they could stand. 



To obtain them a handful of weed was taken and washed in a bucket of water, 

 being vigorously shaken in order to detach all the adherent microscopic organisms. 

 The sediment thus obtained was strained through a coarse silk net, in order to remove 

 the larger particles, and the fine sediment was then bottled and allowed to settle. At 

 first it was of a dull green colour, from the preponderance of blue-green Algae. After 

 an hour or two a red film, like blood, appeared on the surface of the mud. The rotifers 

 have crept out of the mud. After a time they leave the mud and creep up the sides 

 of the bottle into the clear water above ; eventually they reach the surface of the water 

 and there form a ring of red round the bottle. They may then be collected in 

 thousands with a brush and put into clean water. This process may be continued 

 with one lot for days, an hour or two being sufficient time for new hosts of the endless 

 procession to reach the surface. 



Habits. P. gregaria is ordinarily rather a restless animal. It is ready enough 

 to feed, and remains fixed in one spot for a long time, but it swings about continually 

 so that it is not easy to get a good portrait. Though normally anchoring itself, in 

 company with its myriad neighbours, it occasionally casts off" and goes swimming. In 

 Coast Lake it was got in the tow-net, and a few might be seen if a bottle of the lake 

 water was held up to the light. According to Priestley it was much more plentiful 

 in the water of the lake at the Stranded Moraines. 



It was particularly amenable to treatment with mild narcotics. When a very 



