44 JAMES MURRAY 



dilute solution of Eucaine was added to the water, it at once changed both habits and 

 appearance. It ceased its restless swaying about and went on feeding so steadily 

 that it could easily be photographed. The circular muscles were slightly contracted, 

 thus deepening the constrictions between the principal divisions of the body. The 

 foot was inclined to be further retracted than in the normal condition. Otherwise 

 there was little change in form, and the corona was quite unaltered. The effect of the 

 narcotic was much less than on P. laticeps. When that species is treated with Eucaine 

 it partially retracts the foot, expands the usually narrow central trunk, and reduces 

 the width of the corona, in fact it so completely alters its proportions that it is not 

 recognisable for the same species, and might be mistaken for some species of the central 

 group (P. citrina, P. brevipes, &c.) unless particular attention were paid to the spurs. 

 Affinities. P. gregaria belongs to the central group of the genus, possessing eyes 

 and tapering spurs of moderate size. There is nothing distinctive in the general 

 form. The viviparous reproduction distinguishes it from all the species of that group. 

 The red colour is differently distributed from that of P. roseola, in which the red is 

 diffused. In this species it is limited to the stomach. The slender spurs, with broad 

 interspace, are like those of P. laticeps and P. acuticornis. The short antenna 

 separates it from both. It is of larger size than any of the other species in the 

 central group, except perhaps P. citrina. 



The large size, red stomach, viviparous reproduction, and slender spurs set far 

 apart, will distinguish it from all known species of Philodina. The absence of a 

 groove between the prominent collar and the pedicels is also a good character. 



Natural history. As the dominant species in the lakes of Cape Royds the 

 natural history of P. gregaria received a good deal of attention, and many experi- 

 ments were made to elucidate it. These will not be detailed here, but a short 

 summary of the facts will be given.* Its extraordinary abundance must indicate that 

 it is possessed of great powers of resistance to all the adverse influences which would 

 be supposed to attend upon it in such a rigorous climate, or else that it is of remark- 

 able fecundity. It appears to triumph in both ways. 



It is perhaps inaccurate to call it "gregarious." It is found in large " flocks," but 

 it is doubtful if they ever " flocked " together. The great crowds in which they occur 

 appear to arise from the rapidity with which they reproduce themselves. Several 

 young, probably sometimes as many as six or eight, are produced at a time, and they 

 seem to stay and fix themselves where they are born. Thus the patches increase till 

 they reach inches in diameter, and as there is not foothold for all, they stand on one 

 another's heads (so to speak) till a layer of measurable thickness is produced. 



They withstood all the tests applied to Adineta grandis except the heating, which 

 was not tried on them. They are normally frozen in the ice of the lakes for the 

 greater part of the year, and revive at any time that the ice is thawed. When dried 

 and exposed to the lowest air temperatures for a long time, they were not killed, nor 



* The detailed account of the observations and experiments will be found in a paper on " Life under 

 Polar Conditions," in a later number of this series of Reports. 



