42 



MARINE ANIMALS OF MASSACHUSETTS BAY. 



end tentacles project (see Fig. 45), growing more numerous, as 

 in Fig. 46, though they never exceed sixteen in number. As it 

 increases in height constrictions take place at different distances 

 along its length, every such constriction being lobed around its 

 margin, till at last it looks like a pile of scalloped saucers or 

 disks strung together (see Fig. 47). The topmost of these disks 

 Fig. 48. falls off and dies ; but all the others separate 



by the deepening of the constrictions, and 

 swim off as little free disks (Fig. 48), which 

 eventually grow into the enormous Jelly-fish 

 described above. These three phases of growth, 

 before the relation between them was under- 

 stood, have been mistaken for distinct animals, 

 and described as such under the names of Scyphistoma, Strobila, 

 and Ephyra. 



Fig. 49. 



Aurelia. {Aurelia fl.avidula PER. et LES.) 



Another large Discophore, though by no means to be compared 

 to the Cyanea in size, is our common Aurelia (Figs. 49, 50). 

 Its bluish- white disk measures from twelve to fifteen inches in 

 diameter, but its dimensions are not increased by the tentacles, 

 which have no great power of contraction and expansion, and 

 form a short fringe around its margin, widening and narrowing 



slightly as the tentacles 

 are stretched or drawn 

 in. It .is quite trans- 

 parent, as may be seen 

 in Fig 49, where all the 

 fine ramifications of the 



chymiferous tubes, as 

 well as the ovaries, are 

 seen through the vault of the disk. Fig. 50 represents the upper 

 surface, with the ovaries around the mouth, occupying the same 

 position as those of the Cyanea, though they differ from the latter 

 in their greater rigidity, and do not hang down in the form of 



Fig. 48. Ephyra of a Discophore ; Aurelia flavidula. (Ayassiz.) 

 Fig. 49. Aurelia seen in profile, reduced. (Ayassiz.) 



