95 



Fig. 16. 



specimens, fig. 16, showed at the base of the large 

 tentacles slight swellings, which soon developed into 

 short cirri as seen in fig. 17, in Fig. 17. 



which the cirri of the second set of 

 tentacles are also slightly developed. 

 The formula for the youngest Eucliei- 

 lota thus far seen is : 



Ti, 



'2' 



Ti- 



The formula of fiff. 1 6 is : 



Youn^ Euchei 

 lota. 



TTTc/^TTT 



-•-3) -^H -^3' "^J "^2' ''' -"-3' -"-1' -'-a 



and that of fig. 1 7 is : 



JEucheilota, more 



advanced than 



flff. 16. 



Tx, T, 



'4' ^2' ^4' '^' -'-S' -'-1' -^3> 



the third and fourth sets of tentacles being the cirri of the tentacles 

 of the first and second set ; so that the cirri are developed before 

 any additional sets of tentacles are added, the formulae for the 

 number of tentacles of these successive stages being : 

 St=:4Ti + 4^2 = 8L 

 S t = 4 Ti + 4 <2 + 16 Tg = 24 L 

 2 t =r 4 Ti + 4 <2 + 16 Tg + 16 ^4 =r 40 L 

 Among the Geryonopsidce Ag. I have found our Tima formosa Ag., 

 with sixteen long tentacles and sixteen shorter ones, the formula 

 being probably : 



T^, ^4, <3, t^, <25 ^5) ^35 ^4) Tj ; as Tzma never has many ten- 

 tacles it is possible that the young Ti7na have not more than four, 

 or perhaps two tentacles in the first set. The jEquoridcB will give 

 us the best means of ascertaining the order of development of the 

 chymiferous tubes, and of the tentacles in connection with numerous 

 eyes between the tentacles, as these Medusse attain quite a large size 

 before the chymiferous tubes become numerous. From what I have 

 seen in the Berenicidce Esch., the Melicertidce Ag., and the jEquo- 



NoTE A. — The genus Wrightia has but two tentacles when the Me- 

 dusa escapes from the calycles. I have traced the Medusa of our 

 young Wrightia, mentioned by Prof Agassiz on p. 354 of his 4th vol. 

 of Contributions to the Natural History of the United States, through 

 all the stages intermediate between Wrightia and Oceania, and have 

 ascertained that our Wrightia is only the young of Oceania languida 

 A. Ag. described in p. 353 of the same volume. It has at first two 

 long tentacles, then four, in the prolongation of the chymiferous 

 tubes, then eight, sixteen, and finally thirty-two tentacles. The eyes 

 are developed independently of the tentacles ; one pair of eyes mak- 

 ing its appearance for each tentacle. 



