92 
MR. E. C. BOUSJTIELD ON THE 
The first description of any species of Dero is to be found in 
the ‘ Insecten-Belustigung,’ iii. Theil, of Rosel von Rosenhof(2I*), 
published in 1755. Several figures and a lengthy description 
are there given of a species identical with Dero furcata, under 
the name of “das geschrneidige Wasserschlanglein mit zwey 
Grabelspizen.” The remarkable feature of Rosel’s account is 
the moniliform arrangement of the two long palpi by which 
this species is distinguished, which he described. This character 
has not been noticed by Grrebincky, Semper, or myself; but 
the explanation is not far to seek. One of the first signs of 
approaching dissolution in the Naid family is the separation of 
the cuticle from the cells of the epidermis, with formation of 
bullae ; and under these circumstances something of the kind 
has been observed by the writer. It is somewhat curious 
that up to 1877, when the last description of this species was 
written, every observer who described the form gave it a fresh 
name ; so that it has received trivial names from its discoverer 
and from Muller, and scientific ones from Oken, Grrebincky, 
Leidy, and Semper. Rosel observed the process of transverse 
fission in an advanced stage, and described it as a “curious 
method of copulation.” He also described the result of transverse 
sections of the worm. 
Following Rosel, the distinguished naturalist 0. F. Muller (18), 
in 1771, gave a remarkably excellent account of one or two 
species ; all the main features having been grasped, and the 
branchial processes (the characteristic feature of the genus) 
having had their proper function assigned to them. In specific 
characters, however, Muller was less fortunate ; and to him must 
be given the blame of the confusion in the nomenclature of the 
genus which so long existed. In consequence of the small scale 
on which his figures are drawn, there is great difficulty in identi- 
fying the species represented ; but two, if not three, distinct ones 
are certainly shown, all being included under the general name 
of Nais digitata. Rosel’s species is recognized as distinct, 
and named “ the eyeless Naid with pronged tail,” the other 
being called “ the blind Naid with fingered tail.” The distinc- 
tion thus formulated is too slender to enable me to decide 
as to the specific differences ; and in view of the impossi- 
bility of ascertaining the particular species to which Miiller 
intended to apply the name digitata, there seems to be no 
* The numbers in brackets refer to the Bibliography, p. 106. 
