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



cords has the appearance of a row of ganglia connected by bundles of nerve fibres. 

 The size of these ganglia is not quite the same over the whole cord, the foremost being 

 slightly larger than those placed more posteriorly. As to their shape, I observed the 

 following two different types. In some of the ganglia the cells are placed on both 

 sides of the Ijundle, which passes through it, and these ganglia have a very regular 

 rhomboidal form. The other type is represented lay those ganglia in which ganglion 

 cells are to he oloserved only on one side of the nerve bundle, and which accordingly 

 show a triangular form. The triangular ganglia seem to be more numerous in 

 Colossendeis, the rhomljoidal form in Nymphon; in both genera, however, the stout 

 ganglia, which are placed in the front part of the cord, and in the first place the 

 comparatively large ganglion (figs. 6 and 8 y) oliserved by Dohrn are of a distinct rhom- 

 l^oidal form. 



The form of the ganglion is, of course, determined Ijy the number of nerves which 

 branch off from it. The different ganglia give off besides numerous smaller nerves, 

 one (in the triangular form) or two (in the rhomboidal) stouter nerves. These run in 

 the foremost part from the one ganglionic Ijundle to the two others, and form nerve- 

 rings (fig. 6, c&' a"- «'"■ &c.), of which the secondary oesophageal ring (figs. 6 and 8 a) 

 observed by Dohrn is the first and the stoutest. In Nymjohon rohustum I observed five 

 or six of these nerve rings, but in Colossendeis they are still more numerous. 



With regard to the three stout proboscideal nerves, which have been observed already 

 by Semper and Dohrn, and which, according to the latter author, terminate in the three 

 ganglia (the front ganglia of my ganglionic bundles), I have ascertained that they are 

 connected with the ganglionic bundles in the following way : — They run superiorly to and 

 quite independently of the ganglionic Ijundle, till they reach the last but one ganglion of 

 that bundle (fig. 8 u). This they enter, their fibres passing through it and contributing to 

 the comparative thickness of that part of the bundle which unites the last l)ut one and 

 the last of the ganglia (fig. 8 y). However, it is very probable that at least some of these 

 fibres extend Ijeyond the last of the ganglia. I am not quite certam whether perhaps, 

 a union of the ganglionic cord with the proboscideal nerves does not also take place 

 posteriorly. As I have stated akeady al)ove, the proboscideal nerve gives ofi" branches ; 

 and about the middle of the proboscis of Colossendeis prohoscidea, Sab. (sp.), on both sides 

 of the stouter middle nerve two thinner cords run parallel with it in its immediate neigh- 

 liourhood ; these are branches of the middle nerve. Investigating the first part of these 

 lateral branches, close to their origin from the main proboscideal nerve, I once observed 

 (m Colossendeis megalonyx, Hoek) very small ganglia with thin nerve threads runniuo- 

 along this nerve without, however, exchanging fibres ; these are, possibly, the end 

 branches of the ganglionic bundle. While the origin of these branches and their 

 connection with the proboscideal nerves is so easily noticed, with regard to their 

 termuiation I only observed that the Ijundles, when approaching the end of the proljoscis. 



