D. BRYCE ON THE MACROTRACHELOUS CALLIDIN^. 19 



of others, but there is doubtless much to be learned yet both 

 about this and the supposed symbiotic relations to which I have 

 referred. 



The form described by Mr. Milne as the Callidina elegans of 

 Ehrenberg, and which I believe to be quite distinct from the 

 species described by Mr. Gosse under the same name, is by no 

 means uncommon. It usually appears in the trough as a rest- 

 less wanderer, and will crawl about for hours without protruding 

 its wheels. On one occasion I found a colony established in 

 one of my jars, and I discovered that it had the habit of 

 gathering around it, by the continued action of the wheels, a 

 small heap of dirty floccose matter, similar to that made by 

 Rotifer 7nacTOceros, but with this difference, that whereas the 

 latter Rotifer usually perches upon a conferva thread or in the 

 axil of some leaf, the Callidina appeared, in the absence of 

 such convenient spots, to have simply gathered its little pile 

 wherever it might happen to be. I found the little houses 

 lying free among the sediment. 



Mr. Milne has recorded some similar tube-dwelling speci- 

 mens, but does not appear to have made out the species, and I 

 am in the same position with regard to another series of indi- 

 viduals, which were neither the above-mentioned 0. elegans nor 

 any other of the forms familiar to me. 



I have frequently kept specimens of both constrida and 

 quadricornifera for many days in a trough, and have never 

 observed in either the least approach to this tube-making habit. 

 On the contrary, without being w^ild, they, and also miisculosa, 

 lata, and pUcata, do not care to remain long at one spot. They 

 readily protrude their wheels, and will continue feeding for 

 some time, but presently, for some apparent reason, they with- 

 draw their coronae and march, caterpillar fashion, a very little 

 way, and again commence feeding, and so on. Whether it be 

 that they thus endeavour to avoid the accumulation of refuse 

 about them, or that they find that they are attracting the same 

 rejected particles over and over again ; whether they are timid, 

 or perhaps sensitive to the unaccustomed glare of light, I 

 cannot say, but such is their behaviour when under observa- 

 tion. These five species are all moderately common and easily 

 studied. 



There are only two species which swim readily — these are 



