io8 
ZOOLOGY OF THE FAR EASt. 
in a hot-house in England ; the medusa has since been found at several places in 
Europe and in the United States in similar circumstances. A second closely related 
species or subspecies ( C. kawaii, Oka') has more recently been discovered living free 
in the Yangtse-Kiang ; only the medusa is known. 
The medusa Limnocnida seems to be of tropical origin; it has now been found 
in several of the great lakes of tropical Africa, in rivers in western Africa and 
Rhodesia, and in tributaries of the Kistna River in Peninsular India. Three species 
have been recognized, L. tanganikae , Giinther, from the Central African lakes and the 
Niger, L. rhodesiae, Boulenger,^ from tropical South Africa and L. indica, Annandale, 
from India. They are very closely related and may be no more than local races or 
subspecies. Nothing is known of an asexual generation, and the Central African 
medusa reproduces itself by budding as well as sexually, but there is strong circum- 
stantial evidence, in the case of the Indian medusa at any rate;' that a fixed asexual 
generation occurs. The most striking. feature of the medusa is the degenerate nature 
of its manubrium, but both Gravely and Agharkar iop. cit.) and Arnold and Boulen- 
ger* have shown that the mouth is capable of being closed, and does not in life 
remain widely gaping as was at one time believed to be the case. 
Poly podium^ is an extremely aberrant monotypic genus in which the life-cycle is 
complicated, by parasitism (or at any rate semiparasitism) , one stage living attached 
to the eggs of the Sterlet. No medusa is known, but one stage consists of a free-living 
polyp. The species is only known from the River Volga. 
The true relationships of all these freshwater Coelenterates is still a matter of 
controversy. In none except Hydra has the full life-cycle been completely worked 
out, and it is not yet altogether clear to what extent Polypodium has been modified 
in accordance with its peculiar habits. It is not impossible that it may ultimately 
prove to be allied to Annulella and (?) even to Maeotias. 
Craspedacustes and Limnocnida (including, for the sake of argument, Microhydra 
in the former genus) are among the most interesting of all freshwater organisms from 
the point of view of the student of geographical distribution and of the origin of the 
fauna of fresh water. The only localities where Craspedacustes has been found in 
natural circumstances are situated in the Holarctic Zone, and it is perhaps not with- 
out significance that the adult medusa from China was of a more robust habit than 
the one found in artificially-heated ponds. Mayer'* suggests that the former may 
have been introduced into China in the cultivation of ornamental water-plants, but it 
is to say the least a curious coincidence that the aquatic worm Branchiura sowerhyi 
(Beddard), which was discovered at Kew in the same tank as Craspedacustes , also 
occurs in the Yangtse system. Stephenson^ is of the opinion that this worm may 
1 A nnot. Zool. Jap. VI, p. 219, pi. viii {1907). 
? Quart. Journ. Micr. Sci. LVII, p. 427, pi. xlii (1912). 
Gravely and Agharkar, Rec. Ind. Mus. VII, p. 399 (19 12). 
* Proc. Zool. Sac. London 1915, p. 71, pi. 
6 The fullest account of this genus is given by Lipin in Zool. Jahrb. (Anal. Abth.) XXXI, pp. 317-426, pis. xi-xv 
(1911). 
6 Medusae of the World II, p. 366 (1910). 
1 Mem. Asiat. Sue. Bengal VI, p. 87 (1917). 
