DISTRIBUTION OF THE ROTIFERA. 469 



treme range of distribution which these very minute but highly 

 organised animals have attained, and this in spite of the fact 

 that they are essentially fresh-water forms, and that the sea is to 

 them an impassable barrier. 



As regards temperature it appears that though the majority 

 prefer a moderate degree of heat, there are many species which 

 live equally well in cold Arctic and alpine lakes, where the 

 temperature is only a few degrees above freezing-point, and in 

 the warm lakes of tropical countries. But there is no doubt also 

 that some species are able, slowly no doubt, to accommodate 

 themselves to much higher temperatures, and Dr. R. Issel has 

 found ten species, ordinary kinds, living in hot springs near 

 Padua in Italy, at temperatures ranging between thirty-five and 

 forty-five degrees centigrade. 



On the other hand, in Arctic regions, where all water becomes 

 solid during the greater part of the year, the Rotifers, or their 

 eggs, survive the most severe frost, and come to life again as 

 soon as the ice melts. Mr. James Murray informs me that in 

 the Antarctic regions he found at the bottom of a lake on Ross 

 Island, which had been frozen solid for an unknown number of 

 years, a layer of mud containing frozen Bdelloid Rotifers, which 

 recovered and came to life immediately they were |placed in 

 water. In order to reach this bottom layer Mr. Murray had 

 to make a shaft fifteen feet deep through solid ice. This, I think, 

 constitutes a record of endurance for Rotifera. 



To account for such a distribution over the whole of the globe 

 it has been supposed that most species of Rotifera can be dried 

 up, and their bodies carried by the wind, as dust, for long dis- 

 tances, and then come to life again on landing in suitable 

 surroundings. This is, however, a very erroneous generalisation 

 of the fact that a very few species of Bdelloid Rotifera, and in 

 particular Philodina roseola, as first shown by Davis, are capable 

 of secreting, when drying slowly, a gelatinous envelope in which 

 they can resist drought for many months, and come to life again > 

 on being placed in water. This property appears to be confined 



Journ. Q. M. C, Series II. — No. 65. 35 



