COLLECTION OF BDELLOID AND OTHER ROTTFERA. 215 



these two animals, and especially the Bdelloid species, are ex- 

 ceedingly difficult to keep alive after removal from their host. 

 Being apparently merely " lodgers," they do not in any way 

 feed upon their hosts, but I have no doubt that they derive 

 some direct benefit from the water-currents set up by the 

 branchial movements of the latter. When deprived of these 

 currents, and confined in a small cell, they rarely feed and soon 

 perish. 



I come now to the work which I have referred to as outside 

 the ordinary activities of the pond worker, viz. the collection 

 and examination of moss. 



The occurrence of certain Bdelloid Kotifera in moss had been 

 noted by Ehrenberg many years ago, in the Transactions of the 

 Berlin Academy, but only in scattered papers, all, I think, sub- 

 sequent to the publication of his great wovk Die In fusionsthiercheyi 

 in 1838, and these few and unemphasised references seem to have 

 escaped attention either in Germany or elsewhere. The re- 

 discovery by Milne and by Zelinka independently, about 1886, 

 that moss is a favourite home or shelter for such Rotifera, has 

 led to its being more systematically collected for examination, 

 and thus to the discovery of very numerous species which had 

 otherwise in all probability remained unknown. 



Since 1886, the work of searching for moss-dwelling Rotifera 

 has been carried on steadily by several workers, and notably 

 by James Murray, whose untimely loss in the ill-fated Steffansson 

 Expedition is still fresh in our minds. Murray's magnificent 

 use of the opportunities afforded him by the Lake Survey Trust, 

 by the Shackleton Expedition to the Antarctic, and by the 

 Bolivian Boundary Commission has enriched our knowledge of 

 the Rotifera by over a hundred species, gathered in all quarters 

 of the world, and of these the greater number had been met 

 with in more or less direct connection with moss. 



The work which has already been done by the various moss 

 enthusiasts has made a very notable alteration in our concep- 

 tion of the Rotifera in general, and of the Bdelloid Rotifera in 

 particular. Before 1886 the Bdelloida were looked upon as 

 being, like the majority of other Rotifera, inhabitants principally 

 of pools and ditches. It has now become well established, that 



