468 SUMMARY OF CURRENT RESEARCHES RELATING TO 



another to his many services to the students of this group of the 

 Echinodermata by the publication of this list, in which, in addition to 

 the names, we have localities, and a statement of the depth at which 

 the species have been found, as well as references to the principal 

 synonyms and authorities ; there is further a shorter list of the more 

 important works on the subject. 



Coelenterata. 



Nervous System of the Siphonophora.* — Dr. Chun, attracted by 

 the fact that among the Coeleutorata the Hydroid Polyps are the only 

 forms in which no indications of a nervous system have yet been 

 made out, has applied himself to the study of the VelellidaB, and has 

 been rewarded by the discovery of a quite typically diflferentiated 

 plexus of branching and intercommunicating ganglion-cells. To 

 make the relations of this system clear he gives a sketch of the 

 structure of these Siphonophora, into which we cannot here follow 

 him. Subjacent to the whole of the outer ectodermal lamella, there 

 is a plexus of ganglion-cells ; they are only absent where the ectoderm 

 secretes a chitinous support for the air-sac. The cells generally have 

 three or four processes ; more or fewer are rare ; the cell itself is 

 almost completely filled up by the finely granular nucleus; the 

 processes rapidly begin to divide into smaller branches, which again 

 give ofi" a number of lateral branches. The whole is characterized by 

 the straight course which the branches take ; they are not waved or 

 bowed ; freely ending fibres are very rare, for they nearly always 

 unite with the corresponding fibres of other cells. The author was 

 not able to detect any larger marginal nerves made up of smaller 

 fibres, nor any sign of endodermal nervous elements. A further proof 

 that the bodies in question are nervous would appear to be afforded by 

 the fact that there is in them no true connective tissue; this is 

 probably due to the development of chitin. 



Colouring Matter of Medusse.f — Professor M'Kendrick has in- 

 vestigated the properties of the colouring matter of some of the 

 British jelly-fishes — the beautiful blue Cyanea ; CItrysaora, distin- 

 guished by the patches of brown around the tentacles and the margin 

 of the umbrella, and in the long arms; and Aurelia, with the 

 crescentic masses of colour around the ovaries. 



By microscopical examination {^-^ in. x 1200) he ascertained that 

 the colouring matter is not uniformly distributed throughout the 

 protoplasm, but that it exists as little irregularly- shaped particles in 

 the protoplasm of minute cell-like bodies. These granules were about 

 3W^^ in. in diameter ; in Chrysaora of a yellowish colour, while in 

 Cyanea they had a faint tinge of blue. The surrounding protoplasm 

 was colourless. 



It was then attempted to extract the colouring matter. Cutting 

 off the coloured fringes of Chrysaora, portions were placed in 

 (a) strong caustic potash ; (h) absolute alcohol ; (c) sulphuric ether ; 

 {(V) in sea-water. In about an hour the portions in potash were 



* Zool. Anzeig., iv. (1881) pp. 107-11. 



t Journ. Anat. and Physiol., x.v. (1881) pp. 261-4. 



