1902.] NATURAL SCIENCES OF PHILADELPHIA. 753 



evidence to that already put forward by Brooks (1886, p. 300), 

 and others, to show that the hard and fast lines drawn by Haeckel 

 and the Hertwigs separating the " Trachilinie " and the " Lepto- 

 linge," on the ground of anatomical differences or developmental 

 features, are not borne out by Ihe facts. The Hertwigs (1878) 

 hold that " the marginal sense organs (Gehdrorgane) alone furnish 

 characteristics which enable us in every case to distinguish the 

 Trachomedusffi (Trachomedusre and Narcomedusie of Haeckel) 

 from the Vesiculatse (Campanularian medusae) without knowledge 

 of their development." Dr. Brooks has, however, described a 

 species of Laodice which unites in its anatomical features the char- 

 acters of both the Leptoliua^ and the Trachylinse, having the ocelli 

 of the former order and the chitinous gonangium containing medusa 

 buds,* while Prof. Brooks has demonstrated (1886) that it also 

 possesses the true endoderraal sense clubs of the Trachylinse. 



It may be that the present record of observations on Gonionema 

 will be of interest as contributing some new points to the present 

 meagre knowledge of the manifold forms and types which are 

 exhibited iu the developmental processes of this great group. 



Gonosome. 



Gonionema is a very attractive feature of the \Yoods Hole 

 fauna. Its exquisite glassy umbrella, marked with a cross of yel- 

 low or brown by the four radial canals and the gonads, a brilliant 

 row of closely set spots of gleaming phosphorescent green outlining 

 its edge, a fringe of delicate streaming tentacles strung with bead- 

 like clusters of thread cells, are all more or less familiar to many 

 American biologists (PL XXXI, fig. 1). 



On cloudy days or toward nightfall the medusa is very active, 

 swimming upward to the top of the water and then floating back 

 to the bottom. In swimming it propels itself upward with rhyth- 

 mic pulsations of the bell-margin, the tentacles shortened and the 

 bell very convex (PI. XXXI, fig. 2). Upon reaching the surface 

 the creature keels over almost instantly, and floats downward with 

 bell relaxed and inverted and the tentacles extended far out hori- 

 zontally in a wide snare of stinging threads which carries certain 

 destruction to creatures even larger than the jelly-fish itself (fig. 



Agassiz, 1865, p. 125. 

 48 



