66 HYDROIDJE. 



Staurophora) have, like the young Tubularian Medusas, a deep bell and 

 few tentacles ; these characters they lose with advancing age. The 

 young Medusas of the greater part of the Campanularian Hydroids, 

 with the exception of the Eucopidae and some of the vEquoridas, also 

 have, immediately after they are liberated, a form totally unlike that 

 which they eventually assume. A young Clytia or Oceania has a deep 

 bell, only a couple of long tentacles, and few marginal capsules, having 

 a totally different arrangement from what we find in the adult. With 

 advancing age, the tentacles and marginal bodies increase in number, 

 the disk becomes flattened, and ovaries make their appearance alono- 

 the chymiferous tubes. In the Eucopidas the number of tentacles with 

 which the young Medusas are liberated is far greater, the marginal cap- 

 sules being constant in young and old. The same is the case with the 

 ^Equoridas ; they are liberated with many tentacles, and the disk, like 

 that of the Eucopidae, is quite flat. We find also among the Campanu- 

 larians, in some genera, a tendency to localization of the tentacles, as in 

 Eucheilota ; or to great complexity of the marginal capsules, as in Tima 

 and Tiaropsis ; and finally a great development of the gelatinous pro- 

 boscis, as in Eutima, Geryonia, and Tima. The gelatinous prolongation 

 of the disk we must regard as an embryonic feature ; the great number 

 of chymiferous tubes is likewise a character of inferiority ; so that we 

 would place lowest among the Campanularians the Geryonopsidas, all 

 these having tolerably deep bells and few tentacles, more resembling the 

 Tubularians ; next the ^Equoridas, some of which, in their young stages 

 (Halopsis), resemble the Medusas of Tubularians, with their high bell and 

 few tentacles ; next would come the Eucopidas, having still a large num- 

 ber of tentacles, but where the marginal capsules are limited in number, 

 and in which the young Medusas at no time resemble the young Me- 

 dusas of Tubularians ; finally, highest of all the Campanularians would 

 stand the Oceanidas, where the number of tentacles is not very great, and 

 the complication as well as localization of the marginal capsules is very 

 definite. The ovaries likewise guide us somewhat in this classification ; 

 they extend along the proboscis and chymiferous tubes in Tima and 

 the Geryonopsidas ; in the ^quoridas they take their origin from the 

 base of the digestive cavity ; in the Eucopidas they are limited, as well 

 as in the Oceanidas, to definite parts of the chymiferous tubes. 



Were we to judge simply from the nature of the Medusas of the so- 

 called Siphonophoras, the swimming bells and the sexual Medusas, we 

 should be justified in uniting them with the same order as Hydroids, 

 making, of the different orders which had been proposed before, only 

 suborders of the great order of Hydroids, and thus not recognizing the 

 class of Siphonophoras, as recently modified by some naturalists. There 

 is perhaps no stronger case to be brought up in confirmation of this 

 view, than the fact that the free Medusas of Yelella are so closely allied 



