No. I.] THE SENSORY CLUBS. 299 



the most similar families of the two groups. The Geryonidae 

 unquestionably resembles the Geryonopsidae (Eirene, Eutima, 

 and other vesiculate campanularian medusae with a long gastric 

 peduncle) more closely than they do the Aeginadae {Narcome- 

 dusae, Haeckel) in the structure of their gastro- vascular system 

 and reproductive organs, as well as in the shape of their swim- 

 bell. This is especially true of the quadrate Liriope. Most of 

 the Trachynemidae, Rhopalonema, and Trachynema, for exam- 

 ple, bear a remarkable resemblance to the Eucopidae, with 

 which Gegenbaur, relying on their anatomy, has united them. 

 On the other hand, they are separated by so many structural 

 features from the other Trachomedusae that their union with 

 them has hitherto been warranted only by their mode of 

 development. The marginal sense-organs (' Gehororgane ') 

 alone furnish characteristics which enable us in every case to 

 distinguish the Trachomedusae {Trachomedusae and Narcome- 

 dusae of Haeckel'\ from the campanularian medusae [ Vesiculataey 

 Hertwig'] without knowledge of their development." 



" A craspedote medusa with sensory clubs (' auditory 

 clubs'), with sense cells of ectodermal origin while the concre- 

 tions (' otoliths ') are of endodermal origin, may be referred 

 with confidence to the first of these groups, whether the 

 sensory clubs are free on the nerve ring or are inclosed in 

 special vesicles. On the other hand, we may be sure that a 

 medusa in which the marginal sense-organs are composed of 

 vesiculated concretionary ectodermal cells and sensory cells 

 with sensory hairs supplied from the lesser nerve-ring is a 

 campanularian medusa, whether these organs lie in a closed 

 vesicle or in an open pit," 



This generalization is made the basis of the fundamental 

 classification of the veiled medusae by Haeckel, who divides 

 them {System der Medtisen, p. 2) into two Stib-legions : the Lep- 

 TOLiNAE, or " Craspedota, either without auditory organs or 

 with marginal vesicles, or velar auditory-vesicles with ectoder- 

 mal otolith-cells; tentacles usually soft and flexible, primarily 

 hollow; alternation with hydroid polyps probably universal," 

 and the Trachylinae, or " Craspedota, with auditory clubs or 

 acoustic tentacles with endodermal otolith-cells ; tentacles 



