TRACHEARIE. 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 chelicerse and palpi, or only 

 cine 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 Linneeus 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 

 chelicerse 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 + ; 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 labrum, ligula, and two jaws, all soldered together. In 

 this case the palpi belong to the jaws. 



■f- According to Savigny they form the transition from the Arachnides to the Crus- 

 tacea. We place them here, but with some hesitation. 



I 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 Insects of the order of the Parasita. 



