94 



The formula for the number of tentacles of fig. 10 is : 

 S t = 4 Ti + 4 ^2 + 1^ '^s = 24 ^ 



For fig. 12 the formula is: 



S t = 4 Tj -f- 4 <2 + 16 ig + 8 i^ + 8 ig = 40 ^. 



For fig. 1 3 the formula becomes : 



S t = 4 Ti + 4 ^2 + 16 ^3 + 8 <4 + 8 ^5 + 16 ^e — 56 i. 



The presence of eyes does not always modify in such a remarkable 

 manner the order of succession of the sets of tentacles. For in- 

 stance, in Clytia hicophora Ag. (see also Note A, p. 95), we have 

 two eyes between every two chymiferous tubes, and yet the order 

 Fig. 14. of succession is as regular as if the eyes had not 



been present. Fig. 14 is a young Clytia^ just 

 escaped from the calycle, having four long tenta- 

 cles and four rudimentary ones, 2 (fig. 14), and 

 the eyes placed on each side of the middle ten- 

 tacle ; the formula for the arrangement of the ten- 

 tacles is : 



J-15 ^1 '2' ^' 1" 



In fig. 15, the ten- 

 tacles of the third set 

 having made their ap- 

 pearance, the formula 

 becomes : 



Clytia bicopJwra. J-n ^3>6, t^, e, t^, T^. 



Fig. 15. 



Young Clytia Mcophoi'a. 



The formulae for the number of tentacles for figs. 14 and 15 are 

 respectively : 



2 1 = 4 Tj + 4 ^2 = 8 i, and 2 1 — 4 Ti -)- 4 <2 4- 8 <3 = 16 f. 



This Medusa has not been traced farther. I am unable, there- 

 fore, to say whether the succession of the following sets is regular 

 or not. In the genus Eucheilota of McCrady, in which we have eyes 

 and cirri, the following is the order which has been observed : the 

 youngest Eucheilota (probably Euclieilota ventricularis McCr. ; for 

 figure of the adult see McCrady, Proc. Elliot Soc, Plate XI. fig. 3) 

 had four long tentacles, and resembled the young of Clytia, fig. 

 14, so closely that it was at first mistaken for it. More advanced 



