No. 386.] REVIEWS OF RECENT LITERATURE. 161 
it has found lodgment, but some other factor — as yet undiscovered 
— than diminished supply of food and of oxygen, reduction of loco- 
motion, or limitation of growth by pressure, is involved in its pro- 
duction. Whatever the cause, it operates by stopping cell growth © 
and division. The dwarfs are not a permanent race, but are con- 
stantly recruited from the young of the giants. A few specimens 
have been found whose shell structure indicates the growth of a 
typical form from the dwarf condition in consequence of a change to 
amore roomy home. The dwarfs are what they are by reason of 
external conditions and not of inheritance. They present a “ physi- 
ological variety” in which the shape and size of the body, as well as 
the number of cells in the entire organism, are modified by the direct 
action of the environment. There is no evidence that these modifi- 
cations have become heritable. Sexual dimorphism is also well 
marked in C. plana, the average female being about fifteen times as 
large as the average male. As in the case of the dwarfs, the smaller 
size is due to the smaller number of cells in the body. Measure- 
ments of individual cells of the intestine, stomach, liver, kidney, 
muscles, and epithelium show that cell size remains the same in the 
male and female. Whatever the ultimate cause of the smaller size 
of the male, it operates, as in the dwarf, by causing a cessation of 
cell growth and division. EAE. 
British Entomostraca. — The natural history of the fresh-water 
Entomostraca of Epping Forest, a woodland tract of 35,000 acres, is 
given by Mr. D. J. Scourfield, from observations extending through 
a number of years. The author records 102 species, the most com- 
plete local list hitherto published for the British Isles, from which 
a total of 190 species has been reported. One American form, 
Ceriodaphnia scitula Herrick, and several continental species are 
reported for the first time from this region. The cosmopolitan dis- 
tribution of this group is further emphasized by the fact that, with 
one or two doubtful exceptions, all British species occur in conti- 
nental Europe, and most of them have been found in North America, 
and not a few in South America, South Africa, Australia, and New 
Zealand. On the other hand, districts of limited extent, with char- 
acteristic physical features, ofttimes exhibit great differences in their 
Entomostracan fauna. Hydrological rather than climatic factors 
1 Scourfield, D, J. The Entomostraca of Epping Forest, with some general 
remarks on the group, The Essex Naturalist, vol. x (1898), pp. 193-210, 259- 
274, 313-334- 
