92 



Eucope diapJiana Ag. is the only one of this family which I have 



followed from the time of its escape from the calycles to the adult 



state. The young Medusa is liberated with twenty-four tentacles, 



fig. 7 ; its formula would be T^, ^j, i^, <j^, f^, /j^, T^, or, for the num- 



p^jQ y_ ber of tentacles of the first set : 



S t = 4 Ti + 20 <^ = 24 «. In fig. 8, we 

 have the same Me- Fig. 8. 



dusa at the time 

 when the second 

 set is developed. 

 The formula of 

 Young ISucope diaphana. ^^ g is, therefore, 



-'-U '2' ^1) ^2' 'l5 ^2' 'u *2' ^1> ^2» ^1» ^2) -'-I' 



or, for the whole number of tentacles : 



2t=::4Ti 4-20^1 + 24^2 =48f, ^,^ ^ , 



^ ' II 2 J Older Jbucopt tnuphunu. 



and so on, as far as the fifth set of tentacles, fig. 9. 

 The formula for the third set is : 



2 t — 4 Tj + 20 /^ + 24 ^2 -j- 48 ^3 =. 96 f ; 

 that of the fourth set : 



2 1 r= 4 Ti + 20 <i + 24 <2 + 48 ^3 + 48 ?4 = 144 t ; 



that of the fifth set (fig. 9) : 



2 t = 4 T^ + 20 <i -f 24 ^2 4- 48 <3 -f 48 i^ + 48 t^ = 192 t. 



The formula for the arrangement of the tentacles for this last set 

 being (fig. 9), 



-•-15 ^4' ^3' ^5) ^25 h^ hi hi hi hi hi hi hi hi hi hi hi hi hi hi *2> 



hi hi hi hi Tj. 



Fig. 9 is an adult Eucope diaphana Ag., measuring one quarter of an 

 inch in diameter ; at the stage represent- 

 ed in fig. 7, it is not much larger than 

 a pin's head. 

 Jl'MIAMfiinHll^M In the Oceanidce Esch., the presence 

 of eyes between the tentacles, and the 

 development of cirri at the base of the 

 tentacles in some of the genera, modify the uniformity of the order 

 of succession of the sets of tentacles. 



In Tiaropsis diademaia Ag. (Mem. American Academy, Vol. IV. 

 Plate 6), we find two compound eyes between every two chymiferous 

 tubes, the eyes being placed at the same distance from the chymifer- 



FlG. 9. 



Adult Eucojie diaphana. 



