8 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



comet or meteor. When an attempt is made to capture one, it will often 

 escape by going down into deeper water as indeed do other jelly-fish. 

 Escape from observation is all the more easy by reason of the entire 

 absence of pigment excepting for the small amount in the sensory clubs. 

 The yellowish or brownish color usually stated as common in the Cubo- 

 medusae is nowhere present in C. Xaymacana. 



b. External Anatomy. 



2. Form of Bell. C. Xaymacana shows the typical division of the 

 external surface into four almost vertical perradial areas (Figs. 1-3, p), 

 separated by four stoutly arched interradial ribs or bands (Figs. 1-3, i). 

 These ribs thus play the part of corners to the Cubomedusan pyramid. 

 They are formed by the thickenings of the jelly of the exumbrella, and 

 serve to give the necessary strength to the four interradial corners, each 

 of which bears one of the four tentacles at its base. Each rib is further 

 divided into two longitudinal strips by a vertical furrow lying exactly in 

 the interradius (Fig. 2, ifr). The surface of the exumbrella is thus marked 

 by twelve longitudinal furrows, as seen in the same figure (2). Of these, 

 four are the interradial furrows just mentioned ; the other eight are the 

 adradial (afr) furrows, which set off the four perradial surfaces of the 

 pyramid from the four interradial ribs or bands of the corners, each of 

 which is again subdivided, as mentioned above, by the shallower inter- 

 radial furrows. Each interradial furrow ends above the base of the cor- 

 responding pedalium, at about the level of the sensory club ; each adra- 

 dial furrow diverges toward the perradius in the lower third of its course, 

 and thus with its companion furrow narrows down the perradial surface 

 of the pyramid in the lower part of the bell to an area of not much 

 greater width than the niches in which the sensory clubs lie. The pro- 

 jecting interradial corners are of course correspondingly enlarged in the 

 lower part of the bell, and in this way the contours of the surface are 

 changed from those figured in the view of the bell from above (Fig. 2) 

 to those of Fig. 3, which represents a view of the bell margin from below. 



3. Pedalia. From the base of the interradial corner bands spring 

 the four pedalia (Fig. 1, pe), gelatinous appendages of the margin having 

 much the same shape as the blade of a scalpel. These in turn bear on 

 their distal ends, as direct continuations, the long, contractile, simple 

 tentacles. The relatively stiff pedalia have the same relation to the 

 flexible tentacles that a driver's whip-stock has to the long lash. In the 

 living animal the pedalia are found attached to the margin at an angle 



