THE SENSORY CLUBS OR CORDYLI OF 

 LAODICE. 



W. K. BROOKS, 



Professor of Zoology in the Johns Hopkins University. 



By the invitation of Marshall McDonald, U. S. Commissioner 

 of Fisheries, I was enabled to spend the summer of 1888 at the 

 laboratory of the Commission at Woods Holl. 



I found a species of Laodice there in abundance, and as the 

 Hertwigs have been led by theoretical considerations to believe 

 that the incipient stages in the evolution of the velar, ecto- 

 derminal, marginal vesicles of the campanularian medusae 

 ( Vesiculatae, Hertivig) are to be sought for in this genus and 

 its allies, I improved the opportunity to study its bell-margin 

 and velum. 



Other employment has prevented me from preparing my 

 results for publication until now, although they bear upon 

 several general questions. 



I did not find incipient stages in the history of ectodermal 

 sense-vesicles, but I did find evidence that the marginal clubs 

 of Laodice are endodermal sense organs, agreeing in all essen- 

 tials with the so-called "auditory clubs" of those medusae 

 which Haeckel includes in the sublegion Trachylinae ; the 

 Narcomedusae and Trachomedusae. In the marginal clubs of 

 Laodice we have these sense organs in a very primitive and 

 simple condition, which corresponds to the incipient stages in 

 their ontogeny in the Trachylinae. 



This fact does not indicate that the Trachylinae are de- 

 scended from a campanularian medusa like Laodice, but it 

 does show that the distinction between the hydroid medusae 

 and the Trachylinae is by no means so profound and funda- 

 mental as the books would lead us to believe. 



In their account of the marginal vesicles, " Horblaschen " and 

 "Horgruben," of the campanularian medusae, "Vesiculatae," 

 the Hertwigs show that these organs are to be found in several 



