Prof. H. Karsten on Rhynchoprion penetrans. 305 



a little before and underneath the latter. On the first seven 

 abdominal segments these stigmata are narrow circular orifices, 

 like those of Pulex irritans, which lead into equally narrow 

 trachea?, and are surrounded by a narrow six-celled margin 

 (PI. VIII. fig. 7). On the eighth or last complete half-segment 

 there is a stigma, of six times the width of the others, opening 

 into the cloaca, and surrounded by a circle of bristles, which 

 converge over it and close the orifice (PI. IX. figs. 1 & 2). 

 The trachea of this stigma is about twice the diameter of the 

 others, with which it unites on each side of the body to form a 

 common longitudinal stem, from which branches are given off 

 to the organs. 



The trachea? of the female are essentially different, both in 

 number and arrangement, from those of the male ; for in them, 

 besides the great cloacal stigma with its very wide trachea 

 (almost three times as large as the corresponding organ in the 

 male), there are only three very wide trachea? in the seventh, 

 sixth, and fifth dorsal half-segments, with proportionately wide 

 stigmata, which are very similar to the great cloacal stigma. 



The large spines which converge over these wide stigmata of 

 the female, as also over the cloacal stigma of the male, and protect 

 the trachea? from the intrusion of solid bodies, spring from the 

 last tracheal annulus, the peritrema (PI. VIII. figs. 3 & 6); 

 whilst from the annuli of the lun°;-sac or dilatation of the neigh- 

 bouring ends of trachea?, similar spines, standing obliquely erect 

 and reaching as far as the median line (such as are known to 

 occur in Lampijris), appear to assist in the attainment of this 

 object. 



The three next abdominal segments forwards have no stig- 

 mata in the females; but the short first dorsal half-segment 

 attached to the third thoracic segment is furnished on each side 

 with a small stigma analogous to those of the male, and the 

 lateral plates described as lying under the wings are also, as 

 already mentioned, provided with a similar stigma at the supe- 

 rior extremity. 



In the female the three large lateral stigmata, like the seven 

 narrow ones of the male, are situated so near the basal margins 

 of the dorsal plates that they are covered by the posterior mar- 

 gins of the next plates, and are only recognizable by trans- 

 mitted light, when they shimmer through theplate lyingoverthem. 



The four very wide cylindrical main tracheal stems on each 

 side of the abdomen in the female divide each into two branches, 

 one of which unites with the rest to form a stem running along 

 the side of the abdomen, from which smaller branches are given 

 off to the internal organs, which also receive ramifications of 

 the second branch of the main stems. 



Ann. §• Mag. N. Hist. Ser. 3. Vol. xv. 20 



