96 



MR. E. C. BOTJSFIELT) OlST THE 



being one which he identifies with Dero digitata. As there is, 

 however, au absence of anything like a diagnostic description of 

 the species in question, the identity of Dero digitata is still, and 

 probably will remain, unsettled. 



The last contribution to the literature of the subject is the 

 abstract of a paper read by me at the Aberdeen Meeting of the 

 British Association (5). The conclusions therein arrived at hold 

 good only in so far as they are corroborated by the present 

 communication. 



Habits, and Methods of Observation. 



The species of the genus Dero, with the doubtful exception of 

 the form described by Fabricius in 1778, are all freshwater 

 dwellers. They pass their lives entirely below the water-level 

 in tubes which they secrete, and into the composition of wliich 

 foreign matter does not enter. The tubes are as a rule either 

 constructed in the mud, or along the stems of aquatic plants, or 

 even within decayed stalks. 



To this method of life is probably owing the small amount of 

 attention which the genus has attracted. If, however, these 

 worms be present in any locality, they may be easily detected as 

 follows : — 



A portion of the mud, within an inch of its surface, is placed in 

 a bottle to about the depth of half an inch and w^ater added. After 

 the mud has subsided the bottle is allowed to stand for about 12 

 hours, when, if any samples of Dero be present, they will have 

 constructed their tubes in contact with the glass, either in the mud 

 or on the sides of the bottle, and may be removed for examination 

 by pressing on the end from which the head protrudes (as the tail 

 is very easily injured) with a camel-hair pencil. Under this 

 treatment the worm backs rapidly out of the tube, and may be 

 readily secured with a pipette. The species of the genus Dero 

 are sociable in their habits, as many as half a dozen tubes being 

 often placed side by side, and it is quite the exception to find 

 single ones. 



Having secured the worm, the question arises how best to 

 examine it. It is almost impossible to determine the species of 

 any given example when ordinary methods, such as the com- 

 pressorium or the live-trough, are alone employed. In the first 

 case the pressure, even if slight, prevents that full expansion of 

 the branchial area which is absolutely necessary for exact obser- 

 Tation ; whilst in the second case the restlessness of the worm is 



