AJ 4 REPORT—1863. 
I have myself frequently captured in various parts of the British seas a 
medusa which, except in its greater size (0°25 of an inch in diameter) and the 
increased number of its tentacles, so nearly resembles the meduse which are 
thrown off from Laomedea geniculata, or the closely allied L. dichotoma, that 
I have no hesitation in referring it to one of these hydroids as its trophosome. 
The peculiar generative sacs (see fig. 18) were well developed near the middle 
of each of its radiating canals, and in some specimens contained mature ova, 
with germinal vesicle and spot, while in others they were filled with mature 
spermatozoa. 
A similar observation was made by Krohn* on a little medusa which he 
captured in the Bay of Naples, and whose resemblance to the meduse found 
by Van Beneden, as above stated, to be developed from Laomedea dichotoma 
was so close, that Krohn did not hesitate to regard it as the product of some 
similar trophosome. 
Specimens of Corymorpha nutans obtained in tne Frith of Forth, in the 
month of June, were kept alive for some weeks in my tanks. During this 
period multitudes of free medusze were thrown off from them; but though 
the liberated medusz continued to live for a considerable time, and increased 
slightly in size, they never developed any trace of generative elements. In 
the neighbourhood of the locality, however, which yielded the specimens of 
Corymorpha, I captured, by means of the towing-net, a small medusa, which 
I have little doubt belongs to the same species as those thrown off by the 
Corymorpha in my tanks. In the medusa thus found free in the open sea, 
the generative elements, though still immature, were very distinctly visible 
as a pale yellow mass between the ectoderm and endoderm of the manubrium, 
which was rendered tumid by their presence. 
Besides the cases now enumerated, in which the sexually mature medusve 
admit of being referred with certainty, or at least with high probability t, to 
specific trophosomes, there are the very numerous cases in which the gene- 
rative elements have been detected in free gymnophthalmic medusz whose 
trophosome is as yet unknown, or only a matter of suspicion ¢, and whose 
evidence in the present inquiry is necessarily only secondary and indirect. 
I have thus endeayoured to bring together the whole of the evidence, 
which carries us up to a particular point in our investigations. This point 
is of great importance, for its determination enables us to enunciate the fol- 
lowing general proposition :— 
Many species of the fixed plant-like Hydroida give rise, by budding, to free 
gymnophthalnac meduse, which ultimately attain, either directly (the gono- 
cheme) or indirectly (the gonoblastocheme), to sexial maturity, and produce 
ova or spermatozou. 
But the point to which we have thus arrived does not complete the deve- 
lopmental history of the Hyprorpa, and the important question still remains, 
What is the result, immediate and remote, of the development of the ovum 
produced by the free medusa? 
A considerable number of facts bearing upon this question have also been 
accumulated, and the development of the ovum has been traced with more or 
less minuteness by various observers, so that we are now enabled to present 
* Wiegm. Arch. 1851, Erster Band, 8. 265. 
+ It is possible for two medusz to present no differences of even specific value, and yet 
be referable to specifically or even generically distinct trophosomes. (See below, p. 425.) 
See the various systematic treatises on the Medusze, especially Forbes’s ‘ Monograph of 
the British Naked-eyed Medusze,’ published by the Ray Society, 1848; Gegenbaur, “ Versuch 
eines Systemes der Medusen,” Zcitsch. f. wissen. Zool. 1857; and M°Crady, ““Gymnophthal- 
mata of Charleston Harbour,” Proc. of the Elliott Soc, of Charleston, South Carolina, 1859. 
