OCR Text |
Show 818 MR. F. E. BEDDARD ON [Nov. 3, Perrier suggests, that they are the homologues of the nephridia belonging to these segments. Similar glands are stated by Perrier to occur in Perichata, but in this genus it was not possible to observe the external aperture of the glands. Seeing that the buccal cavity is morphologically external, it is not surprising to find that the same glands may in some cases open directly on to the exterior, and in other cases indirectly by means of the buccal cavity. Similar glands are also found in many of the Limicola; Vejdovsky in his ' Monographic der Enchytrseiden'l records their presence in several species of Enchytraus, Anachata, and other genera, comparing them with the "glandes a mucosite " of Urochata. Following upon the pharynx is the narrow oesophagus, which presently widens out in the eighth and ninth segments to form the gizzard, an organ that is found in all Earthworms except in Ponto-drilus. The structure of the gizzard is in no way remarkable: it is surrounded by a very thick circular muscular coat, outside which is a delicate layer of longitudinal fibres ; a few radiating muscles pass through the circular layer ; it is lined by a tall columnar epithelium which secretes a very thick cuticle. The position of the gizzard, placed as it is along the course of the oesophagus, is the same that has been found to occur in all Intra- and Postclitellian Earthworms ; in Lumbricus alone the gizzard marks the posterior termination of the oesophagus. Behind the gizzard the oesophagus is rather wider than it is in front, and becomes extremely vascular ; even in the spirit-preserved specimens which I have dissected, this region of the oesophagus is conspicuous from the abundant presence of blood-vessels, which form two systems :-(1) a superficial plexus, (2) an internal blood-lacuna which surrounds the gut, lying just within the lining epithelium. In relation to the oesophagus are developed certain peculiar glands, which appear to correspond to the " calciferous glands" of Lumbricus. In the common Earthworm (Lumbricus) the hinder region of the oesophagus is furnished with three pairs of lateral diverticula, which have been long known as the calciferous glands, or glands of Morren ; of these the anterior pair are the larger. The structure of these glands has been described by Claparede2; in the region where they are found the oesophagus is extremely vascular, and consists of a number of radiately arranged glands or follicles divided by septa of connective tissue enclosing a blood-space. The calciferous gland itself is merely a diverticulum of the oesophagus, and is made up of exactly the same structures, only the follicles are deeper. Claparede states that he has never observed the formation of the calcareous particles secreted by these glands within the gland-substance. In the genus Urochata, Perrier3 has described three pairs of similar glands, which are of very much larger size than in Lumbricus, but appear to present a more or less similar structure. 1 Loc. cit. p. 29. 2 Zeitschr. f. wiss. Zool. Bd. xix. 18G9, p. 602. 3 Arch. d. Zool. Exp. t. iv. |