18 D. BRYCE ON THE MACROTRACHELOUS CALLTDINJ:. 



be constantly associated with these four species of moss, occur- 

 ring in specimens gathered in the most remote districts of 

 Germany and Austria, and at least in one case in England. 

 But, further, this constant association has suggested that there 

 is a certain benefit accruing to the moss-plants from their 

 affording house-room to these Callidince, and that there is here 

 a true case of symbiosis. We have, in other Rotifera, instances 

 of both the complete and the partial parasitism. To use every- 

 day language, some species are "full boarders," others are only 

 " lodgers," yet neither class gives any return for benefits 

 received. In Callidina symhiotica and C. Leitgebii we have, T 

 think, the first species of Rotifera whose association with 

 another organism has been supposed to be mutually advan- 

 tageous. 



There is no suggestion of symbiosis made with respect to 

 Callidina reclusa, but its life-history is quite as remarkable. I 

 may be allowed to bracket with it for the present purpose the 

 species Boeperi, already mentioned, as having a similar habit of 

 life. These two species live in the cells forming the outer layer 

 of the stems of the small side shoots of Sphagnum. If you place 

 under your microscope such a stem from which you have 

 stripped the leaves you will see that this outer layer consists of 

 elongate cells of some little size, and that many of them possess, 

 usually at one extremity, an opening whose margin is some- 

 times rather elevated, and through which water may freely 

 enter into the cell cavity. These peculiar cells are found by 

 these Rotifers to be exceedingly convenient. There is sufficient 

 space inside to allow them to turn about, and there is a suitable 

 opening from which to protrude their heads when they are 

 hungry, and desire to gather food supplies by the action of their 

 trochal discs. They are protected both from sudden drought 

 and from the atta(;ks of roving enemies. They lay their eggs 

 in the cells, and, indeed, it is probable that under ordinary con- 

 ditions they rarely quit a cell in which they have once estab- 

 lished themselves. They are to be found in nearly every piece 

 of freshly gathered Sphagnum which may be examined, and I 

 have succeeded in keeping a colony alive in captivity for some 

 little time. 



As far as I have yet seen, none of the other forms known to 

 me can be said to prefer any one kind of moss to the exclusion 



