96 
MR. E. C. BOTTSFIELD ON THE 
being one which ho identifies with Dero digitata. As there is, 
however, an 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. 
Halits, 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 which 
foreign matter does not enter. The tubes are as a rule either 
constructed in the mud, or along the stems of aquatic plauts, 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 water 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- 
vation ; whilst in the second case the restlessness of the worm is 
