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Show 532 MR. A. E. SHIPLEY ON SOME [June 19, 3. ASCARIS TRANSFUGA. (Plate XXXV.) Numerous specimens taken from the stomach and small intestine of Ursus arctos, var. piscator. This seems to be the commonest nematode parasitic in the intestine of Bears. Dujardin (' Histoire Naturelle des Helminthes,' 1845, p. 158) describes specimens from the alimentary canal of Ursus arctos and Ursus maritimus, and Linstow in his ' Compendium der Helminthologie,' 1878, adds Ursus americanus and U. labiatus to the lists of its hosts. Blan-chard gives a short description of this species in the ' Annales des Sciences Naturelles,' ser. 3, vol. ii., and a figure of the anatomy of a male. 4. ASCARIS LUMBRICOIDES. A single specimen from the small intestine of Simia satyrus. Note on the Histology of Ascaris transfuga. The histology of Ascaris transfuga has not been described, although the structure of the animal departs in but few particulars from that which obtains in the unusually monotonous group of Nematodes, I have added a few notes on some of the more interesting features. The subcuticular layer of Nematodes has recently attracted a good deal of attention ; in Ascaris transfuga it exhibits the usual structure-that is, it is composed of numerous fine fibrils closely matted together, with occasional nuclei scattered through the mass. The nuclei are small and seem to be degenerating. This subcuticular sheath surrounds the single layer of muscles, and is heaped up along the ventral and dorsal middle lines and around the lateral excretory canals ; it is most abundant in the latter position, especially in the region of the middle of the body; here it shows signs of being divided into two halves by a line which runs from the canal towards the cuticle (Plate X X X V . fig. 1), aud in longitudinal sections it often splits along this line. In this region this tissue with the lateral canal may reach a quarter the breadth of the body, but anteriorly and posteriorly the bands are much more flattened. The dorsal and ventral accumulations of this tissue are much less bulky, only a narrow membrane, compressed between two contiguous muscles, passes from the subcuticular layer and surrounds the dorsal and ventral nerves (fig. 1). Jammesx is of the opinion that this subcuticular layer forms with the nerves a single tissue, whose basis is the ectodermic neuro-epithelial element. He attributes tbe loss of the cellular outline of the embryonic ectoderm to the direct influence of the cuticle, wdiich is formed at a very early stage in the life of the individual, and serves to protect the embryo from the action of digestive juices of the host in which it lives. This explanation of the early formation of the cuticle applies, however, only to the 1 Ann. des Sci. Nat. vol. xiii. 1892, pp. 321-342. |
