TRACHEARI.E. 
317 
FAMILY II. 
PYCNOGONIDES. 
The trunk, in this family, is composed of four segments, occupying 
nearly the whole length of the body and terminated at each extremity 
by a tubular joint, the anterior of which is the largest, sometimes 
simple, and sometimes accompanied by cheliceree and palpi, or only 
one kind of these organs, that constitutes the mouth *. There are 
eight legs in both sexes, formed for running, but the female is 
furnished with two additional false ones, placed near the two ante- 
rior, and solely destined to carry her eggs. 
The Pycnogonides are marine animals f, analogous either to the 
Cyami and the Caprellae, or to the Arachnides of the genus Phalan- 
gium, where Linnaeus placed them. Their body is commonly linear, 
with very long legs, composed of eight or nine joints, terminated by 
two unequal hooks which appear to form but one, and the smallest of 
which is cleft. The first segment of the body, which replaces the 
head and mouth, forms a projecting tube, cylindrical or in the form of 
a truncated cone, with a triangular aperture at its extremity. The 
chelicerae and palpi are placed at its. base. The former are cylindrical 
or linear, simply prehensile, and composed of two joints, the last of 
which is a forceps, the inferior finger, or the one that is fixed, being 
sometimes shorter than the other. The palpi are filiform, and consist 
of five or nine joints, with a terminal hook. Each of the following 
segments, the last excepted, bears a pair of legs J ; but the first, or the 
one articulated with the mouth, has a tubercle on the back, on which 
are placed two eyes on each side, and beneath, in the females only, 
two additional small folded legs, bearing the eggs which are collected 
around them in one or two pellets. The last segment is small, cylin- 
drical, and perforated by a little orifice at the extremity. No vestige 
of stigmata can be perceived. 
* On the siphon of a large species of Phoxichilus brought from the Cape of Good 
Hope by the late M. Delalande, I observed longitudinal sutures, so that it appears 
to me to be composed of the lahrum, ligula, and two jaws, all soldered together. In 
this case the palpi belong to the jaws. 
According to Savigny they form the transition from the Arachnides to the Crus- 
tacea. We place them here, but with some hesitation. 
X M. Milne Edwards, who has investigated the anatomy of these animals on the 
living subject, has told me that in the interior of these organs he observed lateral ex- 
pansions of the intestinal canal, or caeca. I have, in fact, observed traces of them 
under the form of blackish vessels, in various Nymphones. This induces me to 
believe that these animals respire by the skin, a character by which we might form 
them into a particular order, and one perhaps intermediate between the Arachnides 
and Apterous 1 nsects of the order of the Parasita. 
