MALE GROANS OF GENKRATION. 219 



and the anterior aperture the extremity of the cluctus ejaculatorius. 

 Hence the structure of the external sexual organ is as simple as that of 

 the internal ones (comp. 147- II. a. 1). 



The prehensile organ which lies in the ventral plates of the second 

 and third abdominal segments has,, on the contrary, the following very 

 complicated structure. In the first place it consists of three divisions 

 (the same, 4 and 5. A, B, c), the two first of which are placed upon the 

 second abdominal segment, which apparently, at least laterally, consists 

 of two rings ; the third forms the ventral plate of the third abdominal 

 segment. The foremost division (the same, f. 8.) consists of six 

 horny pieces, two anterior triangular smaller ones (a, a), to which two 

 broad, thin, sithe-shaped hooks, which are bent backwards, are attached 

 (c, c), and the two posterior ones (A, 6), which are harder and more 

 horny, and distend about the middle of the upper edge into two dentate 

 knobs. At d the anterior and posterior parts are jointed together 

 (f. 5. represents them extended, f. 8- as bent), and in the centre, be- 

 tween the two pieces of the two sides, there remains a deep unoccupied 

 cavity (f. 4). The second division (f. 4 and 5. B. and f. 7-) consists of 

 two pieces. The larger basal piece, or the ventral plate of the second 

 division of the second abdominal segment, is quadrate, provided at each 

 angle with a small process, which unites it with the preceding and 

 succeeding pieces. Its central surface is deeply excavated, but it rises 

 on each side to a strong obtuse point directed forwards (f. 7- fl )> the 

 posterior edge of which is thickly beset with bristles. Between the 

 two points, consequently in the concave central groove, the second piece 

 lies, which is a geniculated, strong, horny hook (f. 7- b) ; it is united 

 to the first by a joint, and can, by means of muscles, be directed up- 

 wards or withdrawn within the groove. The third division (f. 4 and 

 5. c. f. 6.) is larger than the preceding, and appears as a bellied, ante- 

 riorly concave, horny knob (f. 6. a), which is entirely filled with 

 muscles. These muscles serve to move the anterior hook-shaped ap- 

 pendage, which again consists of two parts, the large, bellied, double- 

 pointed hook (f. 6. Z>), and the thin, cylindrical, double-jointed pedicle 

 (f. 6. c, c) ; this hook, in repose, lies in the anterior excavation of the 

 horny bladder (f. 6. d), but when raised it stands free upon the two- 

 jointed pedicle. A long, thick, pointed, horny bone proceeds backwards 

 from the horny bladder, and it is this which forms the ventral plate of 

 the third abdominal segment (f. 4 and 5. c. e, r.). 



But this entire prehensile organ is only seen when the reflected 



