100 



Fig. 29. 



Adult lAzzia grata. 



then, Ti, «2, Tj 



of the specimens found. It is not till 

 then that we find a second pair of 

 tentacles added on each side of 

 the cluster of tentacles in the 

 prolongation of the chymiferous 

 tubes, as is seen in fig. 29, which 

 represents an adult male Lizzia 

 grata; the size of this Medusa is 

 one quarter of an inch in height. 

 The following formulae would rep- 

 resent these different stages of 

 growth : 



Ti, Ti, or, Str=:4Ti=4<; 

 or, 2 t = 4 Ti + 4 <2 = 8 < ; 



next, Q rp r 



'2 ' -'-I 

 2T, 



I or, 2 1 = 4 Ti + 4 <2 + 8 T3 = 16 «, 



Ti 



Ti 



T:} 2;:} ,i^}or,.t=4T, + 4., + 8T3 + 8. 



= 24 t, 

 (fig. 28.) 



Tx 

 2T3 

 2T, 



I 2tll 



2T3 J.-or, 2t: 

 2T, 



:4Ti+4/2+8T3+8<4+8T5 = 



(fie 



:S2t, 



29.) 



which, to show the arrangement, might be written thus : 



T. T„ 



T, T. 



5 -^3 J-l ^S -'-S' ^4 *2 ^4' -^5 ^3 ^1 -^3 -^5* 



In those Tubularians in which the Medusae are not symmetrical, as 

 in Hyhocodon Ag. and in Corymorpha Sabs (Eu- ^j^ ^^ 

 physa Forbes ?), the order of development is still 

 different from what we have found in any of the 

 preceding species. In a young Hybocodon prolifer 

 Ag., fig. 30, the first set consists of one tentacle only. 

 In Corymorpha pendula Ag., fig. 31, the first set con- 

 sists of one tentacle also, the second set of two, 

 which are formed in the prolongation of the two 

 chymiferous tubes on each side of the first tentacle, 

 and the third set consists again of only one ten- 

 tacle, developed in the prolongation of the chymif- 

 erous tube opposite the first tentacle. In fig. ^1, 

 the tentacles of the different sets are numbered "^^^^'agnified!'*-^"^' 

 according to their order of development. The for- 

 mulae for the above stages of Corymorpha are for the whole cir- 



