164 JOURNAL OF THE [July, 



" The bone is remarkably light and porous. The pores are so 

 large and abundant that they give the appearance of a miniature 

 honey-comb, and pass directly through the substance of the 

 bone, parallel with the longitudinal axis of the vertebral column, 

 leaving only a thin shell of solid bone at either surface of the plate. 

 These pores are slightly fiexuous, frequently branched, usually 

 of an elliptical outline in transverse section, frequently ?(Tth of 

 an inch in diameter, and occasion an extreme example of 

 porosity of bone structure." 



THE MEDUSA. 



Mr. Ludwig Riederer read the following note in explanation 

 of his exhibits of Medusae : 



" Another order of the Polypomedusce is formed by the dis- 

 COMEDUS/E. These are Medusae of considerable size — the edge 

 of the umbrella lobed — the sense-organs covered. The um- 

 brella is thick ; its gelatinous connective tissue is richly devel- 

 oped, and contains a quantity of strong fibrillae and a net-work 

 of elastic fibres, which structures confer upon it great firmness. 

 The edge of the umbrella is divided by a regular number of 

 indentations, usually into eight groups of lobes, between whiqh 

 the sense-organs are contained in special pits. 



"The flat disk of the Ephyra, which is split into eight pairs 

 of lobes, contains a central gastric cavity, into which the canal 

 of the short, wide, four-cornered mannorium leads. From this 

 central cavity there diverge eight canal-like, peripheral diverti- 

 cula (radial pouches), between which there are found the same 

 number of short, intermediate canals (intermediate pouches). 

 At the gastric cavity are placed worm-like, movable tentacles, 

 not found in any Hydromedusce. The marginal bodies, as well 

 as the pit-like depressions (olfactory pits), on the dorsal side 

 of the excavations, in which the marginal bodies are placed, 

 must be considered as sense-organs. They appear in all cases 

 to unite the functions of ocular and auditory apparatus. The 

 auditory function is provided for by a large sack, which origin- 

 ates from the cells of the entoderm, and contains crystals. The 

 eye consists of a mass of pigment, lying on the dorsal, or ventral 

 side near the end of the stalk. 



" Trachymedus^ : These have a body-like cavity, which 



