OCR Text |
Show 1"^ MR. F. E. BEDDARD ON THE STRUCTURE [Mar. 5, The alimentary canal conforms to the type characteristic of this genus. The gizzard, which is distinctly stout, lies in the fifth segment. The oesophagus is rather a narrow tube up to the xivth segment, where it dilates, but still retains its comparatively thick walls and may therefore be still termed oesophagus. A segment or two later (I cannot unfortunately be precise) the thin-walled intestine begins. In the three segments ix., x., xi., there are- one on each-the usual three median and ventral calciferous pouches whose relations call for no special comment; they are apparently common to all the species of this genus. The calciferous glands of the xiiith segment are large and partly encircle the gut. They are imperfectly divided into a dorsal and a more ventrally situated half. From each arises a longish and slender duct which converges towards, and finally unites with the other before its opening into the oesophagus. The two orifices are laterally situated upon the oesophagus. Organs of Reproduction.-As my specimen was rather too large, and not sufficiently well preserved to be conveniently studied by the method of transverse sections, I a m compelled to limit myself in describing the structure of the organs of reproduction to such points as could be ascertained with the help of a lens. As in other species of the genus, the sperm-duct dilates into a large oval chamber immediately after leaving the funnel. This dilatation lies in the xith segment and is attached to its thick posterior wall. In contact with and to the inside of each of these dilatations of the sperm-duct is a thin-walled sac. The two sacs are not fused or even in contact in the middle line, but they represent, I take it, the sperm-reservoirs of other earthworms. They appear to be continuous with the single pair of sperm-sacs through a deficiency in the thick septum, which also allows the oesophagus to pass into the next segment. The sperm-sacs, as is the case with the other species of this genus, are of considerable length and are separable very distinctly into two regions. The total length of each of the two sperm-sacs, in the contracted condition of the worm, is about 30 m m . from the septum to which they are affixed anteriorly to the point upon the intestine where they terminate posteriorly. The posterior more swollen region of each of the two sacs is longer than the almost thread-like anterior portion; it measured 18 m m . The demarcation between the two regions is extremely abrupt, though the posterior part of the sperm-sac has not at that point acquired its full dimensions ; it becomes gradually wider later until it again gradually narrows towards its posterior termination. The dilated region of the sperm-sacs occupies some thirteen segments, where they for the most part conceal the underlying dorsal vessel. Anteriorly and posteriorly, but only for one or two segments at each end, the sperm-sacs are not constricted by and do not bulge out betweeu the intersegmental septa. In the middle of the course of the sacs there are these constrictions, which in the preserved and therefore |