120 THE ANA.TOMY OF IXYERTEBRATED ANIMALS. 



phore contained in a gonangium, somewhat like that of Zao- 

 medea^ is set free as a ciliated bitentaculate body, on the cen- 

 tral axis of which the ova and spermatozoa are developed. 



Fig. 16.— Medusiform zooid of Campanularia (after Gegenbaur) : A, nectocalyx ; te, 

 tentacles ; a. lithocysts; A', velum ; A;', manubrium, inclosing the digestive cavity ; 

 0, mouth ; k^^, radial canals. 



In the genus Aglaophenia (Plmnularidoe)^ groups of 

 gonangia are inclosed in a common receptacle (corbula, 

 Allman), formed by the development and union of lateral 

 processes (comparable in some respects to the hydrophyllia 

 of the Calycophoridoe) from that region of the hydrosoma 

 which bears the gonophores. 



Some medusoids, such as Sarsia prolifera and Willsia, the 

 hydroid stages of which are not at present certainly known, 

 but which are probably coryniform, produce medusoids simi- 

 lar to themselves by budding. The buds may be developed 

 either from the manubrium, or from the marginal canal of the 

 nectocalyx, or from the bases of the tentacula, or even from 

 their whole length. 



In August, 1849, while in the North Pacific, off the Loui- 

 siade Archipelago, I took a species of Willsia (Fig. 17), in 

 which stolons were developed at the bifurcation of each of 

 the four principal radiating canals of the nectocalyx. Each 

 stolon was terminated by a knobbed extremity containing 

 many nematocysts ( (7, g), and gave rise, on one side, to a 

 series of buds, of which those nearest the free end of the 

 stolon had acquired the form of complete medusoids. They 

 had four uabranched radiating canals and four tentacles ; but 

 it is probable that they would assume the form of the parent 

 stock after detachment. 



only a full account of the oro^anization of the group of which it treats, but 

 much inlbrniation respecting the Hydrozoa in general. 



