io6 
ZOOLOGY OF THE FAR EAST 
regarded as organisms that have been established in their present environment for 
a considerable period. 
The only known species of Annulella is one of the small compan}' of solitary 
hydroids. In many respects it is undoubtedly primitive, but this is not the case with 
its tentacles, the structure of which has induced Ritchie ' to classify it provisionally 
in the subfamily Myriothelinae of the family Corynidae. If Asenathia represents the 
sexual generation of the same species this view will have to be modified, but evi- 
dence for the association is still far from complete. Asenathia is undoubtedly related 
to an imperfectly known genus ( Mrt^o/'ms, Ostrooumoff ^) from the mouths of rivers 
entering the Sea of Azov ; possibly it represents a group of Hydrozoa established at 
an ancient period in brackish water. Dicyclocoryne , though very distinct both in 
its hydroid and its medusoid generation from any other genus known, is a much 
more normal unit in the marine family Corynidae; while the two Actinian genera, 
though highly modified and quite distinct from one another, readily find a place in 
the subfamily Metridiinae of the family Sagartiidae ; and to the same subfamily be- 
longs the Gangetic estuarine species Metridium schillerianum , from which, indeed, 
both genera are possibly derived.' 
In Annulella the chief point in which specialization can be definitely correlated 
with environment lies in the production of buds provided with a stout horn}^ cover- 
ing and therefore fitted to survive in circumstances that would kill the polyp. No 
form of specialization is more common than this among freshwater organisms ; among 
the brackish-water animals of the Indian Ocean it is exemplified in the Polyzoon 
Loxosomatoides* and in a still more striking manner in the sponge Laxosuherites lacus- 
tris,^ which belongs to a marine genus and is not notably modified otherwise. 
In Asenathia the most striking adaptive feature is the opacity of the bell. It 
is not quite clear what is the object of this modification but that it has some sig- 
nificance is indicated by the fact that a precisely similar type of colouration'* — if 
colouration it can be called — is found among a number of fish and free- swimming Crus- 
tacea that inhabit the silt-laden creeks and estuaries of the Gangetic delta, for 
example the Bombay Duck {Harpedon nehereus) among the fishes, Leandcr styliferiis, 
L. tenuipes, and a remarkable new species of Palemon which will shortly be described 
in this volume by Mr. S. W. Kemp, among the prawns. 
The essential generic characters of Dicyclocoryne are that the tentacles of the 
hydranth are all capitate and are regularly arranged in two circles and that the 
medusa, whose tentacles are also capitate, lacks ocelli. The only one of these 
characters that seems to be adaptive is the absence of ocelli; in many animals, from 
the Gangetic porpoise Platanista to this medusa, that live in the muddy waters of 
I Rec. Ind. Mus. XI, pp. 543-568, pis. xxx, xxxa (1915). 
« Zool. Am. XIX, p. 30 (1896). See p. 106, postea. 
i Annandale, Mem. Ind. Mus. V, pp. 73-75 (1915). 
■* Id. , ibid. , p. 1 28. 
6 Op. cit., p. 45. Tlie moflification consists, in the case of this .sponge, not in the mere production of bodies of the 
kind but in their high specialization. 
s See Kemp, Hcc. hid. Mus. XIII (ined.). 
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