No. I.] THE SENSORY CLUBS. 303 



It would be interesting to follow out to its logical conse- 

 quences the tacit admission by Haeckel and by the Hertwigs 

 that we find in the structure of the medusae, as medusae, the 

 data for a " system of the medusae " : that they not only fall 

 into families and orders but that they present evidence of 

 the existence of medusae at a time before these orders were 

 differentiated. 



I cannot dwell upon this subject now although I must point 

 out that this admission involves, as a necessary consequence, 

 the further admission that the veiled medusa, as a medtisa, is 

 older than the orders of veiled medusae. 



The Species or Varieties of the Genus Laodice. 



As characterized by Haeckel this genus includes all cam- 

 panularian medusae without marginal sense-vesicles, with four 

 radial canals, four gonads, sixteen or more tentacles, and 

 between them marginal clubs and cirri, or accessory tentacles. 



The genus is widely distributed on both sides of the Atlantic, 

 and A. Agassiz has described as Laodice cellularia {N. Amer. 

 Acalephae, p. 127) a species from the Pacific, of which he says: 

 " I am somewhat doubtful whether this species belongs to the 

 genus Laodicia as the examination of the tentacles could not 

 be made sufficiently accurate to determine this point." 



While it is probable that several species occur in the Atlantic, 

 the differences between them are so slight and there is so much 

 individual diversity that the diagnosis of the species is, in this 

 genus, a very difficult matter. 



Only one of them has been reared from its hydroid. This 

 is Laodice (Lafoea) calcarata of the New England coast, which 

 A. Agassiz has reared from a campanularian hydroid of the 

 genus Lafoea. 



Haeckel says of the Mediterranean Laodice cruciata, this 

 delicate medusa shows so much diversity at different times 

 of the year and at different stages of development, and its 

 extraordinary flexibility and contractility permit it to assume 

 such varied forms, that this single Mediterranean species has 

 received no less than twenty different names, and every new 

 observer has thought he had found a new species. 



