Mr. J. L. Clarke on Lumbricus terrestris. 253 



these two parts, in regard to size, are in the inverse ratio of each 

 other. In Crustacea also, the whole of the pharyngeal, gastric and 

 visceral nerves take their origin from the crura, as was first shown 

 by Audouin and Milne-Edwards. 



The second set of nerves from the pharyngeal collar come off from 

 its posterior half, and communicate with each other by loops before 

 they leave it. The first and largest sends some filaments to the 

 muscular bands of the mouth, upon which they communicate by evi- 

 dent but slight dilatations with the plexus of the ])haryngeal chain ; 

 and after supplying the muscles of the anterior segments, are lost in 

 the integument of the lower hp. The rest take nearly the same 

 course. But what is extremely interesting, the roots of this set — at 

 least of the first and second branches — are continuous across the crus 

 with those of the former set which belong to the pharyngeal chain; 

 and many of their fibres may be traced not only into its ganglia, but 

 through the trunks which proceed from their opposite sides to form 

 the pharyngeal ganglionic plexus ; so that the nerves distributed to 

 the labial muscles and integument of the outer tube, and those which 

 supply the inflected oral and pharyngeal tube, are in direct con- 

 tinuity, not only at their peripheral extremity, but at their roots also, 

 through the common centre which presides over the whole of the 

 digestive apparatus. A similar connexion will be seen to exist with 

 regard to the cephalic nerves. 



The suhventral chain is a double cord gangliated at short intervals 

 by the addition of vesicular substance. Anteriorly the cords are 

 separate and continuous with the pharyngeal crura of their respective 

 sides ; but through the rest of their course they lie in close contact 

 along the middle line. The ganglionic enlargements vary somewhat 

 m size, shape, and approximation at different parts. The vesicular 

 substance is on their under surface, and consists of about two strata 

 of cells continuous in a lamina across both cords. Along their 

 borders, however, the cells form a thicker layer or column, which 

 extends for some distance along the intervening cords. In form and 

 general appearance the cells are similar to those of the phaiyngeal 

 chain, but many of them are larger. Those of the first ganglion extend 

 into the lower parts of the crura, and are continuous behind with the 

 lamina of the second. Each ganglion gives off from its sides two 

 pairs of nerves, which, after sending some filaments to the septa and 

 muscular bands, supply the longitudinal, oblique and circular muscles 

 of the rings. Midway between the ganglia, the mtervening cords 

 give off a single pair, which are distributed to the deep muscles on 

 each side. Within the ganglia the roots diverge in three different 

 ways: — 1, longitudinally; 2, transversely; and 3, to the grey or 

 vesicular substance. The first or longitudinal form a large portion of 

 the nerves, and run in equal numbers in both directions — backwards 

 and forwards, — along the whole breadth of the corresponding cord. 

 In their course, some of them, near the border, separate in succession 

 from the rest and enter the lateral columns of cells ; others proceed 

 as far as the next nerve, with the roots of which they form loops, 

 and pass out, while the rest continue onwards and, perhaps, in sue- 



