754 PROCEEDINGS OF THE ACADEMY OF [DeC, 



1). Gonionema continues this fishing, with little respite, all day- 

 long in cloudy weather. Occasionally it fastens itself to a blade 

 of eel-grass or some other object near the bottom (PI. XXXI, fig. 

 3), or stops midway in its course with tentacles extended, as in 

 my figure (1). In this position it is well-nigh invisible, but a 

 deadly foe to small fish or crustaceans which cross its path. 



Gonads. 



In the mature Gonionema the sexual organs are " frill-like lobes, 

 passing from one side to the other of the chimiferous canal" (Agassiz, 

 1865). Their form and position are shown in PI. XXXI, figs. 3, 

 4 and 5. The free edge of the ribbon of tissue is thickened and 

 rounded, and is bent backward and forward across the radial 

 canal. The color of the gonads has been supposed to afford means 

 of discriminating between the sexes, the males differing from the 

 females in the brighter yellow of the gonadial tissue. But this 

 distinction does not hold, and it is necessary to examine the indi- 

 vidual medusse with a lens in order to separate the sexes. The 

 ovarian eggs, enclosed in the ectoderm of the gonads in the female, 

 give them a granular appearance as contrasted with the more 

 homogeneous and translucent tissue of the male. When a large 

 number of the jelly-fish are separated into two vessels, one contain- 

 ing the males and the other the females, the general color tone 

 of the males is brighter and more lively than that of the females, 

 but the specimens in each dish range all the way from light straw 

 color up through orange, ochre, sienna, to dark brown. 



Embryology. 



It is my purpose to give in outline the main points in the early 

 part of the life-history of Gonionema. I have not discovered that 

 this genus exhibits any notable peculiarities in the development of 

 the egg, and I shall therefore lay the greater emphasis upon certain 

 features of the later developmental stages, which have more signifi- 

 cance in so far as they are le^s familiar. 



A. Dehiscence. — The eggs are imbedded in the ectodermal tissue 

 of the gonad as in a gelatinous matrix (PI. XXXI, fig. 5). The 

 round thickened edge of the ribbon contains the riper eggs, but the 

 thinner portion is well packed with maturing ova. Dehiscence takes 

 place by the breaking down of the superficial ectodermal invest- 



