36 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



perhaps I ought, when treating of the systematic relations of Tripedalia 

 (p. 5, Fam. Ill), to have recognized the analogy to the extent of saying 

 that marginal lobes may not be completely absent from the velarium of 

 Tripedalia. At any rate the gelatinous lobes in the case of Chirodropus on 

 the one hand, and on the other hand the sinuous outline of the margin 

 still mapped out by the lamella in Chirodropus, Chiropsalmus and Tripe- 

 dalia, are certainly very suggestive of an ancestral Cubomedusa in which 

 there was no velarium, but sixteen free marginal lobes instead. Two 

 more indications favor slightly the same view. In both Charybdea and 

 Tripedalia a small notch is seen in the edge of the velarium in the perra- 

 dius (Fig. 44). Its constancy suggests that it may not be a chance or 

 meaningless feature. The second point is the small size of the two 

 marginal pockets adjoining the perradius. These are in the position of 

 the ephyra lobes of the Discomedusas, which always lie on either side of 

 each sensory club, and which do not keep pace with the other marginal 

 lobes in development.' In the Rhizostome jelly-fish especially they are 

 found much smaller than the other lobes, as will be seen by a glance at 

 such figures as Haeckel's for Lychnorhiza (System, Taf. XXXIV, Fig. 2), 

 or for Archirhiza (Taf. XXXVI, Fig. 5), or Hesse's figure of the margin 

 of Rhizostoma Cuvieri ('95, Taf. XXII, Fig. 22). The resemblance between 

 such margins and that of Tripedalia (Fig. 44), with its simple, unbranched 

 velar canals, is very suggestive. On the other hand it must be remem- 

 bered that in considering the vascular lamellae of the internal system we 

 found the indication pointing rather more to Hydromedusan affinities 

 than to any other. Charybdea throws no light on the question, since it 

 has no marginal lobes on the velarium and the marginal pockets end 

 strictly at the margin, so that the only diverticula of the gastro-vascular 

 system in the velarium are the velar canals. 



Before leaving the subject of marginal lobes and pockets I must 

 answer a possible objection that may occur to some careful reader. It 

 may seem that I am wrong in holding that there are two marginal 

 pockets in each octant instead of three, that just as there is one velar 

 canal from each of the smaller perradial pockets (mp', Fig. 44), so each 

 prong of the forked larger pocket (imp), since it is continued into a velar 

 canal, ought to be called a marginal pocket likewise, the whole number 

 of marginal pockets then being twenty-four instead of sixteen. Such a 

 revision of the terminology would not be without some reason in its favor, 

 and perhaps a study of more forms would show it to be correct. But for 

 the present, at any rate, it seemed to me best to abide by the analogy of 



