History of British Entomostraca. 519 
progressive motion which the insect possesses ; and no doubt the 
plumose nature of the filaments assists materially their power, 
though Jurine says that, from their position in the anterior part of 
the body, and from their motions being thus confined by the open- 
ing of the shell, they cannot be considered as acting the part of true 
fins ; and that their use in progressive motion is much inferior to 
that of the anterior pair of feet. Latreille thinks these filaments 
may also act as respiratory organs as well as the branchial plates of 
the jaw. There is very considerable discrepancy amongst the four 
authors I have above mentioned, as to the number of feet. Muller 
and Ramdohr say there are only four ; the former remarking upon 
the singularity of an insect quadruped. Straus enumerates six, 
while Jurine says there are eight. Muller was not aware of the organs 
which Straus calls the third pair of feet ; Ramdohr was, but consi- 
ders them as connected with the male organs of generation, while 
Jurine says that they are organs arising from the matrix, the use of 
which he does not understand. In addition to the first and second pairs, of 
Muller, Ramdohr, and Straus, Jurine considers the organs which 
Muller calls '* barbillons" attached to the mouth, (the palpi of the 
mandibles of Straus) and the branchial plate of the upper jaw, as 
two additional pairs of feet. In describing these parts of the body, 
I shall follow Straus's nomenclature, as appearing to me the sim- 
plest and best, and certainly the most accurate ; the figure which 
Jurine gives of them not being at all correct. Feet, then, are six in 
number, or three pairs. The first or anterior pair (Fig. l.c.c. Fig. 2.) 
are inserted immediately beneath the antennae, are the strongest of 
all, and consist of five articulations.* The penultimate one, or 
" jambe" of Straus, gives origin near to its base to several pretty 
long filaments, varying in number and length in different species ; 
and like those of the antennae, in the larger species, are seen to be 
beautifully plumose, a fact not taken notice of by any author, and 
the last articulation, the tarsus of Straus, is terminated by three pretty 
strong hooks. This pair of feet therefore, by this organization, is 
fitted for both swimming and walking ; the long plumose filaments 
of the fore leg answering the same purpose, and being applied to 
the same use as those of the antennae, causing these feet when put 
in motion to act also as fins, while the hooks at the termination of 
the tarsus enable it to seize hold of the plants, &c. amongst which 
they live, and thus walk from place to place. These feet are con- 
sidered by Jurine as more deserving the name of fins than the an- 
* Jurine says eight. 
