OCR Text |
Show 62 MR. F. E. BEDDARD ON [Feb. 4, looking bodies in most of the posterior segments of the body ; are attached, close to the middle line on either side of the dorsal vessel, to the posterior side of the septa. They were perfectly recognizable both in transverse and longitudinal sections, though naturally their relations to the septum were better shown by the latter, their position with reference to the dorsal vascular trunk by the former series of sections. Structurally these small white bodies consist of a mass of cells continuous with the peritoneal epithelium and probably formed by a local proliferation of its cells ; in the interior of each were a few muscular fibres ; there was no trace whatever of a central cavity, which occurs in the corresponding bodies of the allied genus Acanthodrilus. These " septal glands " were iu Perichceta indica solid throughout. As to Acanthodrilus the observations recorded in this paper were made upon some examples of Acanthodrilus georgianus (Michaelsen, 26), which were collected for me in the Falkland Islands by Dr. Dale, at the request of Mr. Coleman, Secretary to the Falkland Islands Company. This worm differs from all other species of the genus, which I have examined, in possessing a series of sac-like organs connected with the septa. These have the appearance of white solid bodies attached to the septum close to the nephridium-a pair to each segment; they commence at about the 20th segment and continue to the end of the body ; the first three or four pairs are commonly larger than the rest. These organs are not really solid bodies, but sac-like outgrowths of the septa depending freely into the interior of the segments ; they are, in fact, exactly similar to the sperm-sacs and egg-sacs of the same and other Earthworms in their early stages of development; and their absence in the anterior segments of the body, where the sperm-sacs and egg-sacs are found, may possibly be due to their homology with those structures. Each sac has a somewhat racemose appearance owing to the irregular bulging of its walls ; the walls are muscular with a thick coating of peritoneal cells, which are larger and more numerous than those on the adjoining surface of the septum ; the interior of the sac has a delicate lining of peritoneum and communicates with the segment in front by a pore. The only structures with which I can compare these septal sacs are the oval aggregations of peritoneal cells described by Claparede (26) in the common Earthworm. Claparede figures and describes these bodies as consisting of a mass of peritoneal cells enclosing a few muscular fibres; the presence of muscles suggests that the bodies may really be sacs, and not solid proliferations of the peritoneum. Vejdovsky (29) has recorded the presence of similar sacs in Rhyn-chelmis and in Tubifex; but inasmuch as in Tubifex they were only found in a few cases and in the posterior younger segments, Vejdovsky regards them as connected with the growth of the septa. In Acanthodrilus georgianus, as already mentioned, they commence in the anterior region of the body; and as they were found |