SIPHONOPHORA 297 



iu some genera by solid cords of endotlerm. Solinaris sometimes 

 appears in the English Channel, but it is probably a wanderer 

 from the warmer regions of the Atlantic Ocean. It is found in 

 al:)undance during November on the west coast of Ireland. 



Order IX. Siphonophora. 



In this order the naturalist finds collected together a number 

 of very beautiful, delicate transparent organisms to which the 

 general term " jelly-fish " may be applied, although their organisa- 

 tion is far more complicated and dilficult to describe than that 

 of any of the ]\Iedusae. In several of the Hydrozoa the 

 phenomenon of dimorphism has already been noticed. In these 

 cases one set of individuals in a colony performs functions 

 of stinging and catching food and another the functions of 

 devouring and digesting it. In jnany of the Siphonophora 

 there appears to be a colony of individuals in which the division 

 of labour is carried to a much further extent than it is in the 

 dimorphic Hydrozoa referred to above. Not only are there 

 specialised gastrozooids and dactylozooids, but also gonozooids, 

 zooids for propelling the colony through the water (" necto- 

 calyces "), protective zooids (" hydrophyllia "), and in some cases 

 a specialised zooid for hydrostatic functions ; the wdiole forming 

 a swimming or floating polymorphic colony. But this conception 

 of the construction of the Siphonophora is not the only one 

 that has met with support. By some zoologists the Siphono- 

 phoran body is regarded not as a colony of individuals, but as a 

 single individual in which the various organs have become 

 multiplied and dislocated. 



The multiplication or repetition of organs that are usually 

 single in each individual is not unknown in other Hydrozoa. 

 In the Medusa of the Gymnoblast Syncoryne, usually known as 

 Sarsia, for example, there is sometimes a remarkable proliferation 

 of the manubrium, and specimens have been found with three or 

 four long manubria attached by a tubular stalk to the centre of 

 the umbrella. ]\Ioreover, this complex of manubria may become 

 detached from the umbrella and live for a considerable time an 

 independent existence.^ 



If we regard the manul)rium of a ]\Iedusa as an orran of the 

 1 C. Hartlaul), Verlumdl. Dcutsch. Zool. Gcs. 1S06, i>. 3. 



