PROBOSCIS. 59 



sacs had the full complement of stylets, one or two of which equalled the central in size. 

 There appears to be only one explanation of this condition, viz., that the central stylet can 

 be thrown off, and somewhat rapidly regenerated • for it is unlikely that in each case it found 

 its way there from without. Former experience in regard to the stylets shows that such bodies 

 take some time to gain the exterior of the worm, and hence our surprise is lessened at the per- 

 fection of the new structures while the old have not yet escaped from the proboscis. Besides, 

 the anatomy of the parts in A. pulcher will by-and-by throw still further light on the 

 subject. 



In front of the wedge-shaped translucent mass surrounding the basal apparatus of the central 

 stylet is the muscular space (c, Plate XII, fig. 1) previously mentioned, into which the ejaculatory 

 duct opens (at //). This cavity is formed by the folding outwards of the floor of the anterior 

 chamber all round, and it is furnished with a special inner muscular coat. The walls are thus 

 very mobile, and occasionally form an hour-glass contraction in the middle, quite distinct from 

 the narrowing between the sac (whose greatest diameter is in front) and the firm wedge behind. 

 Its anterior border can be carried to the tip of the central stylet ; while in the extruded state of 

 the parts (Plate XIII, fig. 14, e) it forms, when seen from above, a compressed process at each side 

 of the basal apparatus of the central stylet \ more correctly, however, and if viewed from the front, 

 it has the shape of a muscular umbrella, which slopes all round the anterior portion of the 

 latter. M. Claparede does not mention this arrangement at all, and M. de Quatrefages seems 

 to have mistaken it for a pair of glands, which, he explains, probably secrete poison for cankering 

 the wounds inflicted by the stylet, a supposition unsupported by any anatomical basis as regards 

 this spot. Professor Keferstein's structure of the region also requires amendment, since he does 

 not distinguish the separation between the cavity and the floor of the anterior chamber ; thus, in 

 his drawing of the extruded proboscis, the central stylet projects smoothly into the water, and 

 the ejaculatory duct opens directly into the latter a short distance from the stylet. 



d. Granular Glands of the Stylet-Region. 



The glands (w) have the form of lobules, with the long axis of each parallel to that of the 

 proboscis, and are situated beneath the two external layers of the part. The position of the 

 stylet-sacs is always external to these organs. The constituent granules are proportionally large 

 in Tetrastemma, and especially so in Prosorhochmus. I have not found any structural guide to 

 their function, though they are invariably present in the Enopla. 



e. The Reservoir, 



The cavity or reservoir (p, Plate XII, fig. 1) from which the ejaculatory duct proceeds is a 

 somewhat globular or ovoid chamber, with its long diameter for the most part directed transversely ; 

 or it may be compared to the bowl of a short and wide wine-glass, the stem being formed by the 

 peculiar channel of communication with the long posterior region. It is liable to much variation 

 in shape, from the contractility of its inner wall, independently of the action of the massive 

 exterior muscular investment. Extreme contraction of the region transforms the globular 



