78 MANUAL OF ZOOLOGY. 



In Plumularia and some of its allies there occur certain 

 peculiar organs, probably offensive, to which the name of 

 ' nematophores' has been applied. Each of these consists of 

 a process of the ccenosarc, which is invested by the horny 

 polypary, with the exception of the distal extremity, which 

 remains uncovered, and contains many large thread- cells 

 imbedded in it. 



ORDER IV. CAMPANULARIDA. The members of this order 

 are closely allied to the Sertularida ; so closely, indeed, that 

 they are very often united together into a single group. The 

 chief difference consists in the fact that the hydrothecae of 

 the Campanularida with their contained polypites are sup- 

 ported upon conspicuous stalks, thus being terminal in 

 position ; whilst in the Sertularida they are sessile or sub- 

 sessile, and are placed laterally upon the branchlets. The 

 gonopbores also in the Campanularida are usually detached as 

 free-swimming medusoids, whereas they remain permanently 

 attached in the Sertularians. The ova in the medusiform 

 gonophores are usually developed in the course of the gono- 

 calycine canals, and not between the ectoderm and endoderm 

 of the manubrium, as is the case in the Corynida. Examples 

 of the order are Campanularia, Laomedea, &c. The distinc- 

 tions between the Sertularida and Campanularida are certainly 

 insufficient to justify their being placed in separate orders. 

 If united together, it would probably be best to adopt the 

 name Thecaplwra (Hincks) for the order, and to employ the 

 names Sertularida and Campanularida for the sub-orders. 



CHAPTER IX. 

 S1PHONOPHORA. 



SUB-CLASS II. SIPHONOPHORA. The members of this sub- 

 class constitute the so-called ' Oceanic Hydrozoa ; ' and are 

 characterised by the possession of a 'free and oceanic hydrosoma, 

 consisting of several polypites united by a flexible, contractile, 

 unbranched, or slightly branched coenosarc, the proximal end of 

 which is usually furnished with " nectocalyces," and is dilated 

 into a " sornatocyst" or into a " pneumatophore" ' (Greene.) 



All the Siphonophora are unattached, and permanently free, 

 and all are composite. They are singularly delicate organisms, 

 mostly found at the surface of tropical seas, the Portuguese 

 man-of-war (Physalia) being the most familiar member of the 



