126 



MANUAL OF ZOOLOGY. 



little transparent glassy bell, from the under surface of which 

 there is suspended a modified polypite, in the form of a 

 "manubrium" (fig. 51). The whole organism .swims gaily 



through the water, propelled by the 

 contractions of the bell or disc 

 (gonocalyx) ; and no one would now 

 suspect that it was in any way re- 

 lated to the fixed plant-like zoo- 

 phyte from which it was originally 

 budded off. The central polypite 

 is furnished with a mouth at its 

 distal end, and the mouth opens 

 into a digestive sac. From the 

 proximal end of this stomach pro- 

 ceed four radiating canals which 

 extend to the circumference of the 

 disc, where they all open into a 

 single circular vessel surrounding 

 the mouth of the bell. From the 

 margins of the disc hang also a 

 number of delicate extensile fila- 

 ments or tentacles ; and the circum- 

 ference is still further adorned with 

 a series of brightly-coloured spots, 

 which are probably organs of sense. 

 The mouth of the bell is partially 

 closed by a delicate transparent 

 manubrium; bb Radiating 'gastro- membrane or shelf, the so-called 



vascular canals; c Circular canal; ,, ., ~, . , , 



m Marginal bodies ; t Tentacles. VCll. 1 hUS Constituted, these 



beautiful little beings lead an in- 

 dependent and locomotive existence for a longer or shorter 

 period. Ultimately, the essential elements of reproduction 

 are developed in special organs, situated in the course of the 

 radiating canals of the disc. The resulting embryos are ciliated 

 and free-swimming, but ultimately fix themselves, and develop 

 into the plant-like colony from which fresh medusoids may be 

 budded off. The ova in the medusiform gonophores are usu- 

 ally developed in the course of the gonocalycine 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 distinctions between the 

 Sertularida and Campanularida are certainly insufficient to 

 justify their being placed in separate orders. If united to- 

 gether, it would probably be best to adopt the name of Calyp- 

 toblastica (Allman) or Thecaphora (Hincks) for the order, and 



Fig. 51. Free medusiform gono- 

 phore of Clytia Johnstoni (after 

 Hincks). a Central polypite or 



