22 THE MEDUSAE. 



developed, structures are the true rbopalar lappets of Pericolpa, correspond- 

 ing to the i-hopalar lappets of Peripliylla. The large adradial lappets of 

 Pericolpa are, then, in reality tentacular lappets, which correspond, from 

 their position, to the eight adradial arms of the Lucernarida, and to what he 

 believes, from Haeckel's ('80) figures, to be the primitive lappets in the Cha- 

 rybdeida. They are not, however, homologous with the tentacular lappets 

 of Periphylla, but are replaced in this and all higher genera by the adradial 

 tentacles. The tentacular lappets in Periphylla are wholly new formations. 

 The relation, according to Kassianow, of Periphylla to Nausithoe is one 

 of direct descent, the perradial tentacles of the former being replaced by 

 the perradial sense organs of the latter. To this view there are, to my 

 mind, vital objections. To begin with, students are now very generally 

 agreed that the Charybdeida are an aberrant group, showing no close rela- 

 tionship either to the Stauromedusae or to the Coronata. In the second place, 

 there is strong reason to believe that his interpretation of the lappets in Peri- 

 colpa is erroneous. The supposed " sense lappets " of this genus which he be- 

 lieves to be shown on Haeckel's figure are very problematic. Haeckel makes 

 no mention of them, and the structures which he shows might more easily be 

 interpreted as prolongations of the rbopalar pedalia, a view to which, as it 

 seems to me after examining the figures, there is no objection. Furthermore, 

 and of great importance, is the fact that Maas (: 03), who has recently had an 

 opportunity of examining specimens of this genus, makes no mention of these 

 lappets, although he would certainly have been on the lookout for them. It 

 is, then, very improbable that any such lappets exist. Even aside from this 

 essential objection, there are strong drawbacks to any classification based in 

 its essentials on the homologies of such irregular serial parts as the marginal 

 lappets. Indeed, his scheme can hardly include the newly discovered genera 

 Atorella and Periphyllopsis, which, as Maas (: 07) has pointed out, show a 

 numerical condition of the tentacles and lappets incompatible from any 

 reasonable standpoint with Kassianow's concept of their homologies. Still 

 more important is the discovery by Maas (: 03, : 06") of two genera, one (Pa- 

 raphyllina) recent, the other (Paraphyllites) fossil, which, while closely allied 

 to Periphylla in every anatomical respect, show in the radial arrangement of 

 their marginal organs an exact reversal of the ordinary condition. This of 

 course indicates that the significance of the distinction between per- and 

 "inter-radial rhopalia and tentacles is, from the standpoint of phylogeny, not 

 a fundamental one. I cannot better express my views of the actual impor- 



