94 The SiphonopJwres. [February, 



has the form of a cavity filled with a spongy mass 1 of cells, and 

 which seems without representation in the bell of Agalma. This 

 cavity starts from the union of the vessel last mentioned with the 

 stem cavity, and extends through the substance of the bell walls, 

 ending blindly a short distance from its union with the stem. If 

 we look for its homologue in the bells of Agalma, it will be found 

 to exactly correspond in position with the mantel tubes, which 

 are diminutive branches from the vessel which in Agalma con- 

 nects the radial system with the cavity of the axis. This greatly 

 developed mantel tube in the anterior nectocalyx of Diphyes has 

 been called the somatocyst. It is not a float, as far as its homol- 

 ogy goes, although it may, at times, contain globules of oil, 

 which serve to diminish the specific gravity of the animal. The 

 existence of the somatocyst in the bell walls on one side, and not 

 on the other, necessitates a thickening of those lateral walls, 

 which are usually placed uppermost as the medusa floats in the 

 water. The walls on the opposite or lower side are very thin. 

 The thickened upper bell walls, from which the axis hangs, are 

 continued beyond the margin of the bell in order to give a basis 

 of attachment to the stem. This elongation extends over and pro- 

 tects 2 a portion of the posterior nectocalyx, as shown in the figure. 

 It often happens that the posterior bell is ruptured from its connec- 

 tion with the anterior, and but one nectocalyx, with its attached 

 stem, is found. Such a find is liable to deceive a novice in the 

 study of the tubular medusa. It can be laid down as a law to 

 which there is but one exception as yet known, that all the adult 

 Diphyidse have two nectocalyces in their normal condition. 



The second or posterior nectocalyx (pb) differs widely from 

 the anterior in shape and in the character of its chymiferous ves- 

 sels, more particularly in their course through the bell walls. 

 While it has the elongated form of the anterior, the course of the 



Uphv 



Ki-i.lity 



