164 A Bescrii^tion of the Thread-worm, Filaria immitis. 



Turning now to the tail end of the worm, the seat of the intro- 

 mittant organ, it was observed that when viewed laterally it gave a 

 decreasing cylindrical contour (Plate XXXIL, Fig. 14), when from 

 above downward a much broader spatulated character (Plate XXXII., 

 Fig. 15), induced by a spreading out of the sides as from vertical 

 compression, a feature conspicuous throughout the entire spiral 

 portion of the tail end of the animal. As is seen in Plate XXXII., 

 Fig. 14, the outhne of the body following the concavity of the last 

 spiral twist is straight terminating in the tip, while opposed to this 

 the contour is that of a sharp convexity also terminating in the tip — 

 an excess of that characterizing the female tail, and within the tip, 

 at a distance from it of ^^wo of an inch on the straight surface, the 

 spiculum emerges. It is obvious that this arrangement of the 

 parts — the curve of the tail, the flatness of the surface to be 

 brought in direct contiguity with the female, and the thinned-out 

 lateral edges capable of adapting themselves to the sloping sides of 

 her body — must greatly assist in the act of copulation and in the 

 retaining of the male in close contact with the female during the 

 necessary period. The penis or spiculum is a curved, narrow, 

 silicious, somewhat brittle, intromittant organ, bluntly pointed at 

 the free end, bulbous with one, and possibly, two (one on each side) 

 root-hke projections at the base (Plate XXXIL, Fig. 16, g), having 

 a groove along the concavity receiving the vas deferens and stopping 

 short of the tip, and lodged within a membranous sheath (Plate 

 XXXII., Fig. 16, h). The sheath is an elongated capsule con- 

 nected with the cuticle at the genital fissure, is pierced behind by 

 the vas deferens, and has connected with it strong layers of muscular 

 fibres concerned hi the protrusion, withdrawal, and elevation of the 

 spiculum, and derived by modification from the muscular layers of 

 the "tube charnu." Thus, a broad band (Plate XXXIL, Fig. 16, d) 

 is continued from the obhque layer, and is traceable to the base of 

 the spiculum for its retraction after protrusion; another band (e) 

 from the circular layer would tend to protrude the spiculum if 

 retracted, or partially retract it and elevate it if protruded ; while a 

 third band (/) from the longitudinal layer would directly draw it 

 forward when retracted and protrude it ; these layers are doubtless 

 double, one on each side of the worm. The spermatic canal (^) was 

 observed to terminate in a much reduced cahbre tube, a vas deferens, 

 just short of the base of the sheath, being joined at the same time 

 by a horse-shoe tube, one branch of which passed on each side of the 

 sheath and met its opposite member at the extreme end of the tail 

 (Plate XXXIL, Fig. 16, m'' ; Plate XXXIL, Fig. 15, a), being con- 

 nected with the generative appendages (Plate XXXIL, Fig. 16, n). 

 These appendages (possibly vesiculee seminales) were twelve in 

 number, in two parallel rows running longitudinaUy to the body 

 of the worm, and on each side of the spiculum. They consisted 



