364. REPORT—1863. 
can be little difficulty in finding in the body of the polypite the homologue of 
the manubrium of the medusa* ; but the equivalents of the umbrella and gas- 
trovascular canals of the medusa are not at first sight so obvious. I believe, 
nevertheless, that these are not totally unrepresented in the polypite. It will 
be kept in mind that the tentacula of the polypite are merely tubular radia- - 
ting prolongations of the digestive cavity, though with the cavity of the 
tube usually more or less obliterated by the peculiar condition of the endo- 
derm, and that for some distance from their origin they are necessarily in- 
cluded in the thickness of the body-walls of the polypite. Now this included 
portion I regard as the true representative of the radiating canals of the me- 
dusa ; and if we were to imagine the ectoderm of the polypite in a Eudendrium 
or Campanularia to acquire unusual thickness in a zone corresponding in 
position to the roots of the tentacles, we should have a disc-like extension of 
the polypite traversed in a radiating direction by tubular extensions of the 
endoderm which lines the body-cavity of the polypite, and this dise would 
only need to become still further expanded in order to show itself as an un- 
mistakeable umbrella, with radiating gastrovascular canals, while the pro- 
boscidiform extension of the body, which in these genera advances far in front 
of the base of the tentacles, would resemble in all essential points the manu- 
brium of the medusa. 
Now the commencement of such an expansion is evident in the polypite of 
many Campanularide, while in Laomedea flexuosa, Hincks, and Campanulina 
(Laomedea) acuminata, Alder, the ectoderm of the body is actually extended 
as a thin disc for a considerable distance in the plane of the tentacles, which 
acquire in consequence the appearance of being connected at their bases by 
an intervening web. 
While the portion of the tentacles included in the thickness of the body- 
wall of the polypite will thus be the equivalent of the radiating canals of the 
medusa, the free portion of the tentacles is plainly homologous with the free 
tentacles, which in the medusa hang from the margin of the umbrella at the 
points corresponding to the entrance of the radiating into the circular canal, 
and which must be regarded as strictly the continuation of the radiating 
canals beyond their apparent termination in the circular canal. The tenta- 
cles, which in many meduse spring from the intervening spaces upon the 
margin of the umbrella, and are therefore not directly continuous with the 
radiating canals, make their appearance probably in all cases later than the 
others, and are frequently less developed. These must be placed in the same 
category with the lithocysts as simple marginal appendages, to be carefully 
distinguished from the primary tentacles, and, like the lithocysts, have no 
representative in the polypite. 
* Huxley (‘Oceanic Hydrozoa’) strongly insists on this relation, and is so impressed 
with the closeness of the homology, that he uses the same term, “ polypite,” for both. 
Agassiz (op. cit. vol. iv. p. 226) has witnessed the very simple adelocodonie gonophore 
in male specimens of his Rhizogeton fusiformis, stead of withering away after the discharge 
of its contents, elongate itself, develope tentacles, and become transformed into a polypite. 
I have myself, on one occasion, seen an analogous phenomenon in the female gonophore of 
Cordylophora lacustris, in which, after the discharge of the ova, the spadix had become 
elongated through the ruptured chitinous investment of the original gonophore, had deve- 
loped an ectoderm, thrown out tentacles from its summit, and become metamorphosed 
into an ordinary polypite. In the case of Cordylophora the transformation is confined to 
the spadix, while, according to Agassiz, the entire gonophore of Riizogeton takes part in 
the metamorphosis. 
I believe that in both cases the phenomenon is an abnormal one ; it certainly is so in 
Cordylophora, for, in the ordinary conditions to which this hydroid is exposed, no meta- 
morphosis of the kind takes place. 
