ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 401 
dichotoma and L. geniculata—meduse referable to the type of Obelia, Pér.— 
sexual elements are never directly developed. For this purpose there is needed 
a new zooid (fig. 17 9 and fig. 18) which no longer presents the developed me- 
Fig.17.—Medusa of Cam- _ Fig. 18.—Reproductive sac (sporosac) budding 
ponularia — Johnstoni from the radiating canals of the gonoblasto- 
shortly after liberation cheme of Obelia (Laomedea) geniculata. 
from the gonangium, 
illustrating the pecu- 
liarities of the gono- 
blastocheme. 
a, portion of umbrella and, 8, radiating canal of the 
medusa ; ¢, spadix of sporosac; d, wall of sporosac, con- 
sisting of endotheca alone; e, ovum, with germinal vesicle 
and germinal spot; jf, ovum, with numerous germinal 
spots in the germinal vesicle. 
dusal type, but, instead of it, the type of the 
adelocodonic gonophore. This zooid springs as 
a bud from the radiating canals of the medusa, 
and is constructed upon precisely the same plan 
as that which we meet with in the gonophore of 
Clava or Hydractinia, except that the ectotheca 
|e would seem to be absent. It has an axile 
Ss o., inaipientaporcsac, spadix (fig. 18 ¢), whose cavity 1s in direct com- 
formed as a bud upon the ra- | ™unication with that of the radiating canal from 
diating canal. which it springs. Immediately investing the 
spadix are the generative elements, ova or sper- 
matozoa; while these are themselves surrounded and confined by a true endo- 
theca (d), which becomes at last ruptured for the liberation of its contents. 
The zooidal nature of these buds is nowhere more distinct than in the genus 
Aglaura, Pér., a form not yet traced to a polypoid trophosome. Here the 
generative elements are produced in eight sac-like processes which surround 
the base of the manubrium, which is itself borne on the extremity of a stalk 
dependent from the summit of the umbrella. These sacs are undoubtedly . 
true buds, and are entirely homologous with the gonophores of Clava ; and 
it is plain that they are developed from the proximal extremities of the 
radiating canals, just where these canals pass off from the manubrium in 
order to run along the sides of the stalk before reaching the umbrella.* 
* See Leuckart’s description of Aglaura Péronii (Wiegmann’s Archiv, 1856, Erster 
2D 
