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Show 1894.] NEMATODE PARASITES. 533 parasitic forms, and does not include the numerous cases of free-living Nematodes, unless we are justified in assuming that the latter are descended from parasitic forms. Bohde ' describes the contractile part of the muscle-cells of Ascaris as consisting of homogeneous pillars, arranged in two radial rows on the outer side of each fibre; between these pillars is an " Interfibrosmasse," the fibrils composing which are continuous on the one hand with the fibrils of the spongioplasm of the medullary part of the muscle-cell, and on the other with the fibrils which compose so large a part of the subcuticular tissue. In the dorsal and ventral longitudinal ridges the fibrils of the subcuticular layer form a sheath round the nerve-cords. The exact function of this fibrillar tissue which so closely connects different systems of tissues is still obscure, but as Bohde points out, in criticizing the work of Apathy (and the same applies to Jammes), it can hardly be nervous in function. M y sections of Ascaris transfuga confirm the work of Bohde. Thus in Nematodes we have a very intimate connection between the subcuticular tissue (ectoderm) and the muscular and nervous systems. The best account of the nervous system of Nematodes is contained in Hesse's paper " Ueber das Nervensystem von Ascaris megcdocephala." 2 The lateral nerves which he describes, lying on each side of the lateral line, are in Ascaris transfuga very large at the anterior third of the body, and lie surrounded by the heaped up subcuticular tissue which forms the lateral line; behind they diminish in size and are difficult to distinguish from the subcuticular tissue in which they are embedded. At the posterior end nerves again became conspicuous in the same position; these are the bursal nerves connected with the ventral median nerve and they run forward along the lateral line. I believe them to be connected with the anterior lateral nerves by a very fine filament. The lateral lines are continued beyond the opening of the cloaca and at the extreme posterior end pass into one another. In this region of the lateral lines the cells, which more anteriorly seem to be degenerate and show little or no structure beyond a broken-down nucleus, are more distinct. The alimentary canal consists of three very clearly marked regions-the muscular oesophagus, the intestine, and the proctodeum ; these pass suddenly into one another (figs. 2 and 4). Of these three divisions the intestine is by far the longest; it is lined throughout by the familiar high columnar epithelium, which does not change in character from one end to another. Both inside and out this tube is lined with a well-marked cuticle, which on the inner surface is frequently charged with vacuoles or vesicles, which seem to make their way into the lumen of the tube in which many of them lie freely (figs. 1 and 3, Plate X X X V . ) . The nuclei are arranged 1 " Apathy als Eeformator der Muskel- und Nervenlehre," Zool. Anz. no. p. 38. 2 Zeitschr. f. wiss. Zool., Bd. liv. PROC. ZOOL. Soc-1894, No. XXXV. 35 |