,28 DISCOVERY REPORTS 



holotype agrees more closely with the specimens from WS 228, e.g., as regards width 

 of trunk and length of abdomen (see ratios above). The third leg is incomplete ; but the 

 sum of the segments measured exceeds the trunk length, so that the complete leg would 

 probably be about half as long again as the trunk. 



The holotype has a much longer proboscis than any of the Discovery specimens, 

 being almost as long as the sum of the first two segments. P. magnirostre, Mobius 

 (1902, p. 194, pi. XXX, figs. 12-14), from Kerguelen also has a very long proboscis and 

 may prove to be identical with P. magellanicum. It is possible that more than one 

 species of Pycnogoniim is represented, but the five specimens measured above are not 

 sufficient to enable one to settle this point satisfactorily. 



Distribution. Off the Falkland Islands and Gough Island. 



THE CENTRAL NERVOUS SYSTEM IN DECOLOPODA 



The nervous system is very similar to that described for Colossendeis by Hoek (1881, 

 pp. 108-119, pi. xvii, fig. 2 and pi. xviii, fig. 4). The long circum-oesophageal com- 

 missures, considerably foreshortened in Fig. 73 A, enclose the oesophagus and a pair 

 of somewhat triangular muscles that work the proboscis. 



The usual main nerves arise from the supra-oesophageal ganglia, namely: a, a median 

 azygous proboscidial nerve ; b, a pair of optic nerves each dividing into three branches 

 to innervate the anterior eye, the "sense organ "i and the posterior eye respectively 

 (see Fig. 73 C), and r, a pair of nerves to the chelophores. A pair of fine nerves, d, 

 probably correspond to those designated by Wiren (1918, pp. 73 and 79, figs. 10, 14 

 and 15) as nerves No. 3 in Nymphon grossipes-mixtum^. But, instead of pursuing a 

 course parallel to the azygous proboscidial nerve, as in Nymphon, they pass obliquely 

 outward and forward towards the base of the chelophores, innervating the muscles that 

 work these appendages. Near to these latter nerves, a pair of thin strands arise {e) and 

 run directly forwards to break up into a meshwork innervating the skin along the 

 anterior border of the cephalon. In D. aiitarctico this pair of nerves is well seen 

 (Fig. 73 B, e), but in the dissections of D. atistralis they were, as a rule, removed with 

 the skin. D. antarctica differs from D. atistralis in two respects: (i) the optic nerve is 

 much stouter, with shorter thicker branches; (2) nerve d arises from the optic nerve. 

 In the specimen from which Fig. 73 B was obtained, nerve d arose from the base of the 

 median branch of the optic nerve on the left side, as represented in the diagram, whereas 

 on the right side it arose from the main stalk of the optic nerve just below the forking. 



From the first thoracic gangUonic mass three pairs of nerves arise (Fig. 73 A, i, 2, 3) 

 innervating the proboscis, palps and ovigers respectively. In D. antarctica from St. 42 

 the proboscidial nerves arise each from the circum-oesophageal commissure a short 

 distance from the thoracic ganglionic mass; in the male from St. 149 the nerve on the 



1 Probably a vestigial eye (see Loman, 1924, p. 318). 



- Only present in Nymphon (Wiren, 191 8, pp. 73 and 77). 



