﻿PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 197 



" The ventral nerve goes obliquely outward and backward to the space or joint 

 between its own segment and the one in advance, penetrates the branchial leaf-limb at 

 the part or moiety of its own side, distributes many filaments to the basal joint, and is 

 continued on through the second and third joints, before being finally resolved in the 

 fourth and terminal joint (PL XXXIV n ix — xn). More minute filaments are sent off; 

 usually between the origins of the two chief nerves, from the four ganglions. 



"The terminal ganglion (0, Pis. XXXIV and XXXV) represents the coalescence 

 of the nerve-centres of at least three segments. Its anterior dorsal pair of nerves (n 18, 

 PL XXXVI) traverse the interval between the fifth (xn) and sixth (xni) thoracetral 

 apodemes, in a course more obliquely backward than the antecedent pairs. The corre- 

 sponding anterior ventral nerve (n xiii, Pis. XXXIV and XXXV) supply the sixth pair 

 of leaf-limbs or fifth branchial pair (xni). Below the origin of this pair, nervous filaments 

 (r, PL XXXIV) pass off to the lower fourth of the intestine. 



" The second ventral pair (n xiv, ib.) is chiefly distributed to the fibres of the flexor 

 muscles of the tail-spine, arising from and occupying the soft, rather tumid tract, which 

 resembles a leaf-foot soldered down to form the covering of the hindmost part of the 

 ventral surface of the thoracetron. 



" The third pair of principal nerves from the terminal ganglion represents a bifid 

 continuation of the neural axis (PL XXXV, /). After a course of about three lines 

 each sends off a nerve (n xv, ib.) belonging to the ventral series, which supplies the 

 hindmost or postanal region of the abdomen, affording the articular surface for the tail- 

 spine. 



" After sending off the above nerve, each continuation of the chord forms an oblong 

 loop (ib., k), which, prior to the removal of the vascular sheath, looks like a ganglionic 

 swelling; 1 beyond which the chord (X, Pis. XXXIV and XXXV) continues along the 

 side of the tail-joint, and, on entering the cavity of the tail-spine (c), resolves itself into a 

 fasciculus of fine nerves (ib.,pl.), resembling the 'cauda equina' of anthropotomy. But 

 in this bundle a principal filament, or continuations of the chord (PL XXXIV, /m), can be 

 traced about a third of the way down the spine. These nerves seem to constitute the 

 major part of the tissues in the hollow of the spine, and render a marvellous supply of 

 neurine to so hard, inflexible, and seemingly insensible a part. 



" Each chord, X, from the ganglionic loop sends off nine nerves, four directed towards 

 the ventral (PL XXXV, fig. I, pi.), four towards the dorsal (PL XXXIV, fig. 1, a 1—4) 

 region of the spine : the ninth nerve, being of larger size, claims to be the continuation of 

 the bifid neural axis. If the dorsal and ventral divisions be regarded as those of four nerves 

 serially homologous with such divisions of antecedent primary pairs, they would indicate 

 as many segments coalesced in the fore part of the spine. The ninth nerve and its 

 divisions supply in a similar way the rest of the tail-spine. 



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1 As represented by Vander Hoeven, op. cit., pi. iii, fig. 2 c. 



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