1902-1903.] Fresh- Water Mites. 41 



sirous of acquiring some little glory by the discovery of a new species. 

 But the result was not answerable to my desires. Not even a single 

 Hydrachnid was offered to me by a single person." 



In fact, says Muller, the most eminent entomologists held 

 the Hydrachnas in the utmost indifiference, as though it were 

 a credit to them to be totally ignorant of the subject. 



This book is very nicely got up. It contains 82 pages 

 of letterpress, and 11 plates with 71 figures, all well en- 

 graved and printed. It is also hand-coloured. In all, Muller 

 describes and figures 49 species. When we consider the 

 microscopes in use in Muller's time and compare with our 

 own, it is a fine piece of work, and shows how much Muller 

 was in love with his subject. 



Muller described the mites all under one generic name 



Hydrachna — the differences being shown in the specific name 

 only. Now, Hydrachnidse is the name of the family, but 

 Hydrachna is still retained as the name of one genus only. 

 Piersig gives a list of a number of Muller's mites which have 

 now been placed under their proper generic names, while 

 still retaining, as they should do, the specific names given by 

 their author. 



The first writer to give another genus, I believe, was 

 Fabncius in 1805, who introduced the name Atax. Since 

 that date one generic name after another has been added, 

 until now we have, I think, 60 in all. At least, Piersig in 

 'Das Tierreich,' 1901, gives 57 genera, and I believe two or 

 three have been added since. The species have also multi- 

 plied at the same rate, the number being now, in the words 

 of Dominie Sampson, "prodigious." One genus alone, 

 Arrhenurus, has a hundred certain species and about fifty 

 doubtful, and the list is still increasing. 



Of course, the specific differences in some of these water- 

 mites are very small— indeed so much so, that I doubt if 

 Miiller with the instruments at his command could have seen 

 them at aU. I have often had to boil mites in liquid potash 

 to see the necessary structure for the identification of the 

 species. 



There is something, however, I think, of much more import- 

 ance to study than the mere naming and identification of 

 species, and that is the life-history of these beautiful mites 



