OCR Text |
Show 1885.] NWW-ZEALAND EARTHWORMS. 819 There are certain glandular structures prespnt in all three species of Acanthodrilus, which appear to represent these three calciferous glands of LAimbricus and Urochata. In A. nova zelandia and in A. dissimilis, in the thirteenth segment the oesophagus undergoes a remarkable alteration in its character ; it apparently widens considerably (PI. L I I. fig. 2,gl), and this saccular dilatation, when cut open, presents an appearance somewhat like that of a ruminant's stomach ; a number of leaf-like folds project into the lumen of tbe tube. In the following segment the oesophagus is again somewhat dilated (fig. 2, gV) before it returns to its original calibre ; a series of transverse sections (PL LII. fig. 1) shows that these supposed dilatations to the oesophagus are distinct glands, which are separated from its walls anteriorly and posteriorly ; in the middle their lumen is directly continuous with the lumen of the oesophagus without the intervention of a duct. The glands of either side are quite separate from each other ; on the dorsal side of the oesophagus the two glands of each pair nearly come into contact, being separated only by a very narrow space, in which the dorsal vessel and the short mesentery connecting it with the gut lie. Ventrally the glands of each pair are widely separate. The posterior pair of glands differ from the anterior in being trilobate. Each is divided by horizontal furrows, coinciding with the long axis of the body, into three separate lobes. The anterior pair of glands are unilobate, and considerably smaller than the posterior pair; otherwise their structure is the same. The accompanying drawing (PI. LIT. fig. 1) will give a correct notion of the appearance of the posterior pair of glands under a low power. In Acanthodrilus multiporus there are apparently only a single pair of calciferous glands present (PL LII. fig. 3,gl), the specialization of which has gone a step further; instead of being little more than mere dilatations of the oesophagus, the calciferous glands of this species are quite separate from the oesophagus, communicating with it only by a short narrow duct. The structure of these glands appears to be identical in all three species. They consist of numerous lamellse concentrically arranged, reaching from the walls of the gland to its opening into the oesophagus; these lamellae are, however, of different lengths, as will be apparent from the drawing (Plate LII. fig 1). In Lumbricus Claparede figures the lamellse of equal lengths. The lamellse consist of a core of connective tissue, in which is a large blood-lacuna, and on either side a row of cells which secrete the calcareous corpuscles, and with which they are filled, as also is the lumen of the gland. Clapr.rede did not succeed in observing the calcareous corpuscles in course of formation, although he found the lumen of the gland and the oesophagus full of them. The structure of the calciferous glands of Urochata, judging from M . Perrier's description and figures, appears to be different; instead of a series of lamellse, there appear to be a quantity of closely-packed csecal tubes. The folded structure of the calciferous glands of Acanthodrilus |