116 THE VOYAGE OF H.M.S. CHALLENGER. 



of the inner surface of the skin. Now, this inner surface of the integument both of the 

 body and the legs, especially in si^ecies of the genus Colossendeis, is richly furnished with 

 ganglia, which spread all over it, and are connected wth nerves. They are so very 

 numerous as to form a continuous network of ganglia and nerves, their function being, 

 I believe, to innervate the cavities of the integument, for which I have suggested a 

 respiratory function. There can therefore l^e no difficulty in supposing that the ganglia 

 of my ganglionic bundles are derived from originally integumentary ganglia, and that 

 their high development is to be attributed to the changed functions of the parts which 

 surround the mouth. 



While these same ganglionic bundles, in a more or less developed state, are found 

 in all species and genera of Pycnogonida, it is very probable, I believe, that in the other 

 classes of the Arthropoda their homologues' will be sought for in vain. The shape of the 

 terminal ganglia, of which the dorsal one is the largest, is best seen from the drawing 

 (PI. XVIII. fig. 8). Of the nerves which arise from it, two run in an oblique direction 

 (one to each side), these enter again (at least in Npnj^hon) a small ganglion, from which 

 nerves are given off to the tactile organs placed in the so-called lips of the proboscis. 

 Of these small ganglia, those two, which are placed on both sides of one of the lines of 

 union of the three jjroboscideal parts, are again connected by means of a nerve string. 

 The tactile organs consist of a small tuft of hairs placed just at the end of the chitinous 

 list which marks the place of union of two of the proboscideal parts meeting there 

 laterally. Perhaps the nerve fibres of the small nerve bundles, which enter the secondary 

 ganglia and innervate these tactile hau--tufts, take their origin in the three original 

 proboscideal nerves. 



Besides the three original nerves and the three ganglionic bundles, two thinner 

 nerves enter the proboscis dorsally. These I observed only in Nij-niphon arising from 

 the supra-CBsophageal ganglion. The two thin nerves which in Colossendeis run along- 

 side and quite near to the main proboscideal nerve must be considered as branches of 

 this main nerve, and no doubt there are still other longitudinal nerves, which run 

 through the proboscis, and which must also be considered as branches of one of the three 

 main nerves. 



What I observed in regard to the remaining part of the nervous system is the 

 following : — The shape of the four thoracic ganglia may be seen from the figures on 

 Plate XVII. The length of the commissures uniting these ganglia is different in 

 different genera, and even in the different species of one genus. In Nym2ohon rohustum, 



' It seems to me that an analogous case is that of the visceral or stomatogastric nerves of the Crayfish, studied by 

 different authors, and investigated recently more accurately by Prof. Huxley (Anatomy of Invertebrated Animals, 

 London, 1877, p. 330), a complex nervous apparatus, serving chiefly for the innervation of the muscles of the mandibles, 

 <and lor that part of the intestine which has been called by Huxley the gastric milL This gastric mill of the Decapod 

 Crustacea is placed behind the cosophageal commissures ; the analogous apparatus of the Pycnogonids is found in front 

 of the same commissures. 



