1894.] XEMATODE PAEASITES. 533 



parasitic forms, and does not include the numerous cases of free- 

 liviug Xeniatodes, unless we are justified in assuming that the 

 latter are descended from parasitic forms. 



Rohde 1 describes the contractile part of the muscle-cells of 

 Ascaris as consisting of homogeneous pillars, arrauged 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 .Rohde points out, in criticising the 

 work of Apathy (and the same applies to Jammes), it can hardly be 

 nervous in function. 



My sections of Ascaris transfuga confirm the work of Rohde. 

 Thus m Xeinatodes 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 Xeinatodes is 

 contained in Hesse's paper " Ueber das Xerven system von Ascaris 

 megaloc&phala" 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 sub- 

 cuticular 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 procto- 

 deum. ; 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 XXXV.). The nuclei are arranged 



' " Apathy als Reforruator der ITuskel- und Nervenlehre," Zool. Anz. no. 439, 

 p. 38. 



2 Zeitschr. f. wiss. Zool., Bd. liv. 



Pkoc. Zool. Soo.— 1894, Xo. XXXV. 35 



