66 IIYDROID^. 



Stauropliora) have, like the young Tubularian Medusa3, a deep bell and 

 few tentacles ; these characters thev lose with advancintr aaie. The 

 young Medusas of the greater part of the Campanularian Hydroids, 

 with the exception of the Eucopida; and some of the ^Equoridaj, 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 along 

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

 which the ^oung Medusa; are liberated is far greater, the marginal cap- 

 sules beins: constant in youn<f and old. The same is the case with the 

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

 that of the Eucopida^, 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 ])ro- 

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

 of the disk we must regard as an embrj^onic feature ; the great number 

 of chymiferous tubes is likewise a charact<ir of inferiority ; so that we 

 would place lowest among the Campanularians the Gcrvonopsida?, all 

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

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

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

 few tentacles ; next would come the Eucopidai. having still a large num- 

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

 and in which the young Medusa? at no time resemble the young Me- 

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

 stand the Oceanida?, 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 cla-ssification ; 

 they extend along the proboscis and chymiferous tubes in Tima and 

 the Geryonopsidje ; in the yEquorida^ they take their origin from the 

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

 as in the Oceanida^, to definite parts of the chymiferous tuljes. 



Were we to judge simply from the nature of the Medusa) of the so- 

 called Siphonophora?, the swinuning bells and the sexual Medusa^, we 

 should be justified in luiiting them with the same order as Ilydroids, 

 making, of the difl'erent orders which had Ijeen proposed before, only 

 suhoi'ders of the great order of Ilyilroids, and thus not recognizing the 

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

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

 view, than the fact that the free Medusa? of Velella are so closely allied 



