Vil FRESH-WATER FORMS 205 
Bathynomus giganteus and Encephaloides armstrongi, and the 
loss of the larval development. Owing to the similarity of 
conditions in the deep sea all over the globe most of its inhabit- 
ants are universally distributed. It is also a striking fact that 
species are found in the deep sea of the tropics whose nearest 
allies occur, not in the littoral seas of the tropics, but in those of 
the temperate region. This fact has already been alluded to 
in dealing with the distribution of the Lithodinae. Alcock! 
remarks that between 50-500 fathoms in the Indian Ocean are 
found Crabs such as Maia, Latreillia, and Homola, regarded as 
characteristic of the north temperate seas; the lobster Mephrops 
andamanica, taken at 150-400 fathoms, is closely allied to the 
Norwegian WV. norwegica ; and nine species of “ Schizopoda,” which 
are certainly temperate forms, occur in the Indian Ocean at 
depths of 500-1750 fathoms. 
B. Fresh-Water.” 
If we except the Crayfishes and River-crabs, the Crustacean 
fauna of running water is exceedingly poor, but in all standing 
fresh-water, from the smallest pond to the large lakes and inland 
seas, Crustacea, especially Entomostraca, are abundant and charac- 
teristic, and form an important item in the food of fresh-water 
fishes. In small ponds a vast assemblage of Cladocera is met with : 
these animals multiply with great rapidity by parthenogenesis, 
especially during spring and summer, but on the advent ot 
untoward conditions sexual individuals are produced, which lay 
fertilised winter-eggs which lhe dormant until favourable condi- 
tions again arise. As Weismann first pointed out, the frequency 
with which sexual individuals are produced in the various species 
is closely correlated with the lability of the water in which 
they live to dry up; so that the Cladocera which inhabit small 
ponds usually have at least two “epidemics” of sexual individuals, 
one during early summer and the other before the onset of winter. 
Besides Cladocera, the Phyllopoda (e.g. Apus, Artemia, etc.) 
1 A Naturalist in Indian Seas. 
2 Scourfield, J. Quekett Micr. Club, 1903-4, gives a useful list of British Fresh- 
water Entomostraca. For the identification of fresh-water Cladocera, Lilljeborg’s 
“Cladocera Sueciae,” Nov. Act. Reg. Soc. Upsalensis, 1901; for Copepoda, Schmeil’s 
‘Siisswasser Copepoden,” in Bibliotheca Zoologica, iv., v., and vili., 1892, 1893, 
and 1895 are recommended. 
