ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 413 
medusz, which he saw liberated from the gonangium of Campanularia John- 
stoni, Alder. He seems, however, not to have been aware of the nature of 
these bodies, which were afterwards observed in the same species, and cor- 
rectly interpreted, by Wright *, who also witnessed the generative sacs on the 
radiating canals of the medusa of Obelia (Laomedea) dichotoma just after 
separation +. 
I can fully confirm these observations on the medusa of Campanularia 
Johnstoni, having myself on more than one occasion witnessed the generative 
sacs budding from the radiating canals of meduse shortly after liberation from 
the trophosome of this hydroid (see fig. 17). 
In a Campanularian hydroid which I discovered in the Firth of Forth, and 
would refer to Van Beneden’s genus Campanulina, under the name of C. re- 
pens, Allm., I found the generative sacs distinctly developed on the radiating 
canals of the medusa at the time of its liberation from the gonangium. 
Dujardin ¢ has seen ova produced in the walls of the manubrium of Cla- 
donema, a medusa traceable to a hydroid trophosome nearly allied to that of 
Coryne, and which Dujardin names Stawridium (Stauridie). These ova were 
observed in specimens of a Cladonema thrown off from Stauridium in his 
tanks, so that the observation is continuous and complete. 
Krohn§ has seen ova and spermatozoa produced in the walls of the manu- 
brium of the female and male medusa-buds of a hydroid, which he believes 
to be identical with the Podocoryne carnea of Sars. The generative elements 
had indeed in this case made their appearance at a very early period, for 
their rudiments were manifest while the medusa was as yet incompletely de- 
veloped, and still attached to the trophosome |}. 
To the facts above stated I am enabled to add the case of Coryne eximia, 
Allm., in whose medusa, just after liberation, from specimens obtained in 
Shetland in July 1862, I saw the generative mass in the form of a minutely 
granular substance included between the ectoderm and endoderm of the 
manubrium, and having nucleated spherical cells scattered through it. These 
cells are in all probability the germinal vesicles, with their germinal spot, but 
with the yolk not yet differentiated around them. 
The cases now stated contain, I believe, the whole of the instances in 
which free meduse, giving rise to ova or spermatozoa, have been traced by 
actual and continuous observation to the hydroid trophosome. 
Evidence, however, scarcely less convincing, is afforded by those cases in 
which, though the free medusa in which the eggs or spermatozoa are found 
cannot be traced by direct observation to a trophosome, its resemblance to 
forms which have been so traced is so close as to justify us in assigning to 
both a similar origin. 
Desor {| found, swimming freely in immense numbers in the port of Boston, 
United States, a Sarsia-like medusa, which he did not hesitate to identify 
specifically with a form which some weeks before he had seen produced by 
buds from a Coryne obtained in the same locality. In the free meduse now 
obtained, the walls of the manubrium were swollen by the development in 
them of ova or spermatozoa. He was able to trace the ova through all the 
stages of segmentation. 
* Edinb. New Phil. Journ. 1858, vol. vii. p. 286. : 
+ Op. cit. 1859, vol. ix. p. 115. ¢ Ann. des Sci. Nat. 1845. 
§ Wiegm. Arch. 1851, Erster Band, p. 263. 
| In medusx, however, thrown off from specimens of Podocoryne carnea in wy tanks, 
no trace of generative elements could be detected, even at the end of fourteen days 
after their liberation. 
§| Ann. des Sci. Nat. vol. xii. 1849, p. 207. 
