74 M. Hesse un a new Parasitic Crustacean. 



The abdominal segments, when in their normal state (that is to 

 say, neither much contracted nor much extended), are perfectly 

 distinct from each other ; they decrease in depth and width from 

 the base to the apex, and are nearly square, being only a little 

 'narrower above than below. The last, or sixth, does not at all 

 resemble the others in its form, which is nearly that of a shield, 

 widened at its base, slightly emargi'nate at the sides, and termi- 

 nated by two obtuse points furnished with a few hairs. Seen in 

 profile, they show between them a cavity in which the anal 

 orifice opens. However, these forms, which are well marked 

 when they are in their normal state, are extremely variable and 

 become considerably modified according to circumstances. 



The head, seen in profile, has the frontal margin truncated at 

 the apex and rounded and bent downwards at the sides. Upon 

 it we perceive the antennae, which are thick, short, cylindrical, 

 and composed of two or three joints, terminated by divergent 

 hairs. Starting from the antennae, the outer margin of the 

 cephalic envelope descends obliquely in a straight hne to go to 

 the superior angle formed by the inflation presented by the 

 orifice of the oesophagus. 



Between these two points is the buccal orifice, which is placed 

 in the centre of a circular platform slightly hollowed in the 

 middle. This apparatus, which is very complicated, presents 

 the following arrangement : — Immediately below the antennae, 

 and at the sides of the epistome, there are two pairs of footjaws, 

 which are solid, pectinated, and terminated by a hooked claw; 

 then follows, in the middle, the buccal aperture, composed of a 

 conical proboscidiform tube, which issues from and returns into 

 a cavity formed in the centre of the platform. This tube, which 

 is constructed of a very firm, but very delicate and transparent, 

 membranous tissue, receives its impulsion from two pairs of 

 footjaws, one superior and one inferior, which keep it extended 

 or contracted according as this organ issues from or re-enters 

 the cavity destined for its reception. When the tube is entirely 

 out, we may perceive in its interior a conical appendage, rounded 

 at the end, ascending and descending frequently, like the piston 

 in the chamber of a pump : this is really the mouth with its 

 mandibular armament. 



The latter is formed of two pairs of footjaws, which are denti- 

 culated and trenchant, and furnished with a corneous substance; 

 these, by applying themselves together, can seize and triturate 

 objects. They are, moreover, surrounded by a soft and mobile 

 labial margin, which seems to cover them when necessary; 

 lastly, within these organs we see some mandibular palpi, com- 

 pleting this system, which may be employed, according to cir- 

 cumstances, both for suction and mastication. 



