BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 327 



muscular space (e, various figures) into which this duct opens, forms a kind of sac 

 that is occasionally distended with the cells and granules, before they reach, 

 through the central pore, the pit of the anterior chamber. 



The cavity or reservoir (g, Plate IX. fig. 3, and other figures), from which the 

 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 stern being formed by the peculiar channel of 

 communication with the long posterior chamber. 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 cavity into a mere transverse slit. Its inner surface is 

 provided with a series of glands, the larger and more distinct having minutely 

 granular contents (Plate IX. fig. 3, c), and easily distinguished from those of the 

 anterior chamber or long posterior gland. Towards the opening of the ejaculatory 

 duct the glands are smaller than in the swollen part of the reservoir, and they 

 again decrease in size before the organ narrows to its posterior channel of com- 

 munication. In this comparatively large chamber the dancing granules, hereafter 

 to be described, have free scope for the display of their movements, and not only 

 do they move themselves, but they cause such large bodies as the compound gland- 

 cells from the posterior chamber, when they happen to be present, to revolve and 

 jerk also, a state of matters that has probably helped to mislead M. de Quatre- 

 fages as to the ciliation of the organ. Such, however, is very distinct from 

 ciliary motion. The reservoir diminishes posteriorly, so as to form in the con- 

 tracted state of the parts a very narrow duct (0), which by-and-by expands, and 

 becomes continuous with the long glandular posterior chamber, the whole form- 

 ing an hour-glass contraction, as represented in the various figures. 



Before, however, proceeding with the description of the posterior chamber, it 

 may be as well to complete the narration of the structure of the two translucent 

 regions in which the foregoing duct and cavity lie. 



In addition to the ejaculatory duct of the reservoir, the anterior division 

 possesses also the central stylet and its peculiar arrangements, with the external 

 circlet of granular glands. The former projects straight forward in the usual 

 state of the parts, and is generally about the same size as the largest stylet in the 

 lateral pouches, with which it likewise agrees in structure and composition 

 (Plate IX. fig. 3,&c). Its point under examination seems generally to project 

 into the pit of the anterior chamber, though the thick muscular floor occasion- 

 ally closes round it. The base of the stylet is fixed to the granular sac (X) ; 

 the arrangement being not inaptly likened by Dr Johnston to an awl, the anterior 

 or smaller end of the sac sending its investing substance over the head of the 

 stylet, and grasping part of the spike. The basal sac (or awl-handle) is narrowed 

 anteriorly, gradually widens backwards, is then marked by a constriction, and 



