440 FERNAXDUS PAYNE. 



independently of hydroids. Originally such studies were neces- 

 sary, no doubt, but I see no reason why they should continue. 

 Neither do I see how we can arrive at a satisfactory classification 

 until we know the complete life-history of each form studied. 

 This may seem a rather discouraging viewpoint, since we now 

 know the life-history of so few, and when we consider the 

 enormous amount of work and the difficulties involved. 



Mayer ('10), in his classification of the medusae of the world, 

 describes the Leptomedusae as follows: gonads on the radial 

 canals; otoliths, if present, of ectodermal origin; medusae arise 

 through alternation of generations from Campanularian hydroids. 

 He describes the Trachymedusae as medusae having marginal vela, 

 uncleft bell margins, and lithocyst concretions of endodermal 

 origin. In all textbooks we find statements that Trachymedusae 

 are without a hydroid stage. 



Where then does Craspedacusta ryderi belong in our present 

 system of classification? Lankaster ('81), Douglas ('12), Mayer 

 ('io), and others have placed Craspedacusta among the Trachy- 

 medusae. Allman ('80) placed it among the Leptomedusae. On 

 the other hand Giinther ('94) described it as a medusa descended 

 from Leptomedusan ancesters, which had developed sense-organs 

 with an endodermal axis independently of the Trachymedusae. 

 Mayer ('10) regards the Trachymedusae as transformed actinulae. 

 He says: "They (Trachymedusae) commonly develop through an 

 actinula larva in which the bell grows out as a collar-like, or 

 intertentacular lappeted expansion from the sides of the body 

 after the tentacles have appeared, and the tentacles of the 

 actinula become those of the medusae. The medusa of the 

 Leptomedusae is formed upon a different plan, for the tentacles 

 grow outward from the bell-margin after the bell has developed. 

 I believe, therefore, that the bell of the Trachymedusae is not 

 homologous with that of the Leptomedusae. It is evident that 

 the endodermal otoliths of the Trachymedusae are not homologous 

 with the ectodermal otoliths of Leptomedusae. I believe that the 

 medusa-shape has been acquired independently in the Trachylina 

 and Leptolina forms of veiled medusae." 



Microhydra, along with Protohydra and others, has either been 

 placed in a separate subdivision of the Hydromedusae, or with 

 the Tubularian hvdroids. 



