9 8 The Siphonophorcs. [February, 



ical covering-scale ; its surface is convex with one side flattened 

 and the base concave for the lodgment of the sexual bells and 

 retracted tentacle. There are no radial vessels in this covering- 

 scale, and only the central cavity (I) of peculiar cellular appear- 

 ance, representing the somatocyst. At the fundus of this cavity 

 there is generally found an oil globule (og) which it is unneces- 

 sary to say has no morphological relationships with the float of 

 Agalma and its allies. A similar globule is also found at the 

 base of the somatocyst near the point of attachment of the young 

 Eudoxia to the stem of the Diphyes, before the rupture of the 

 fragment took place. 



The structure of the covering-scale of Eudoxia betrays at once 

 the homology of the central tube of the covering-scales of other 

 Siphonophores, as well as of the somatocyst of the anterior bell 

 of Diphyes. The covering-scale of Eudoxia resembles the ante- 

 rior bell of Diphyes except that it has no radial system of ves- 

 sels and no bell cavity. The somatocyst of the swimming-bell of 

 the Diphyes is represented in its fragment, Eudoxia, by the central 

 cavity (I) of the large covering-scale. This cavity is in turn the 

 same as the central tube of the covering-scales of all other 

 Siphonophores. When we recollect what has been pointed out 

 above in relation to the homology of the somatocyst to the man- 

 tle vessels in the nectocalyces of Agalma, the true homology of 

 the covering scale and the nectocalyx becomes evident. If this 

 view of the morphology be a correct one, the comparison of the 

 covering-scale with the asymmetrical bell of a hydroid like the 

 genus Hybocodon, is not correct, or at least its medially-placed 

 tube does not correspond with a radial tube in the bell walls of 

 the hydroid medusa. 



The under side or base of the conical covering-scale of Eu- 

 doxia is very concave, and in this recess hang, when retracted, 

 the remaining structures of the animal. The largest (b) of these 

 bodies is a nectocalyx whose outer walls are crossed by four 

 longitudinal ridges, serrated on their edges and continued into 

 projections beyond the bell cavity. Two of these ridges, corre- 

 sponding with those found on the under side of the posterior 

 nectocalyx of Diphyes, are more prominent than the other pair, 

 and enclose a canal in which the polypite, tentacle and sexual 

 bell, lie when retracted. The bell cavity is deep, filling almost 

 the whole interior of the nectocalyx, and along its surface pass 



