HYDROZOA. 47 



panularia, for example, columnar gonoblastidia 

 arise in the angles between the stem and branches 

 of the coenosarc, or from the sides of the branches 

 themselves (figs. lo and 19). The lower portion 

 of each gonoblastidium forms a sort of peduncle, 

 above which the cuticular investment of its ec- 

 toderm becomes separated as an urn-shaped cap- 

 sule, the ^gonotheca.' Such capsules, or "ovigerous 

 vesicles," are very variable and beautiful in form. 

 True gonophores, protected by the gonotheca, are 

 borne along the sides of its axial column. 



In some Calycophoridce and PhysopJioridce, 

 particular regions of the hydrosoma may devote 

 themselves to the performance of the reproductive 

 function, and, becoming separated from the rest 

 of the fabric, subsequently undergo a surprising 

 amount of modification. 



Finally, in the Lucevnaridce, with the exception 

 of Lucernaria and a few closely-allied genera, the 

 reproductive bodies are produced by fission from 

 polypites of almost microscopic minuteness ; and, 

 in their detached condition, grow with such ra- 

 pidity as ultimately to attain a weight of many 

 pounds, or even hundreds. A corresponding ad- 

 vance in structure attends this vast increase of 

 size. Each, at the outset of its free existence, 

 includes a complete transverse segment of the 

 polypite from which it has separated. This soon 

 forms a lobed swimming organ, or umbrella, with 

 the hooded lithocysts before mentioned. From 

 the centre of the umbrella hangs a large polypite, 

 whose lips, in such genera as Aurelia, Cyaiiea, 

 and Chrysaora, form lobes of considerable length, 

 the folds of which serve as temporary receptacles 



