476 GEOLOGICAL SURVEY OF THE TERRITORIES. 
during a rather brief duration the sensory threads on the tips of the 
antenne become nearly three times longer than before the beginning of 
domestication. 
We now find in comparing the fresh-water generations with the salt- 
water generations of Daphnia rectirostris that the latter generations not 
only changed in consequence of the immediate effect of the surrounding 
elements, but also in consequence of retarded development under their 
influence; and, furthermore, that the sexual maturity shows itself earlier 
in the salt-water generations than the complete typical development of 
the body parts. The termination of the sensory antenne, the color of 
the body, the lesser pinnulation of the bristles in the salt-water genera- 
tions are principally dependent upon the immediate effect of the sur- 
rounding elements. The smaller number of the above-mentioned spines 
on the postabdomen principally depends upon the retarded develop- 
ment under the influence of changed surroundings. In the latter case 
the individuals commence, without awaiting the development of their 
body parts, to augment, and are in that state a complete animal form. 
Branchipus ferox attords a still more characteristic example of the in- 
fluence of the salt-lake element. Milne-Edwards,! whose words Grube? 
repeated in his diagnosis of this species, gives a brief description of 
Branchipus ferox from the neighborhood of Odessa. Chyzer?® completed 
his description from Hungarian specimens. The diagnosis by Chyzer 
of this species differs so much from that of Milne-Edwards that both 
authors could not possibly have had one and the same form of Branchi- 
pus, as we shall see later on. It is difficult to understand why Milne- 
Edwards does not mention the two so important characters of this 
species, which ought to rank with the principal characters which Chyzer 
enumerates. This is the conspicuous length of the egg-sac, and espe- 
cially the tact that the abdominal appendages or fureal lobes are bristled 
only on their inner edge. To this latter peculiarity Chyzer especially 
points out the characteristics of Branchipus ferox. It is evident that 
Milne-Edwards had a very closely allied form to that of Chyzer’s, since 
in the neighborhood of Odessa, wherefrom Milne-Edwards’s form came, 
generations of this species occur in salt, brackish, and fresh water, which, 
owing to their dependence of the density of the water basins, consider- 
ably differ in their characters. The generations inhabiting salt-water 
ditches of about 5° Beaumé differ as much from the individuals inhab- 
iting fresh water, especially the Hungarian forms described by Chyzer, 
as any Species will differ from another one. Had I not found all pos- 
sible transitory forms between fresh-water and salt-ditch forms, had I 
not convineed myself of the variability by domestication of this form, 
I should have regarded the salt-lake specimens as a new form. For 
some time I really took them for a variety of Branchipus ferox Chyzer. 
At present, and after so many convincing results, I can only condition- 
ally regard this form as a variety. 
To demonstrate how much the salt-lake generations of Branchipus 
Jerox (from the salt-water ditches) differ from the Hungarian fresh- 
water specimens, compare the following characters: The egg-sac of the 
salt-lake Branchipus jerox reaches in its length only to the beginning, 
or to the middle, of the fifth apodous segments, but as the following 
sixth, seventh and eighth segments are longer than the anterior seg- 
ments, the egg-sac reaches scarcely to the middle of the postabdomen, 
e 
1H: stoire naturelle des Crustacées, III p. 369. 
2Bemerkungen tiber die Phyllopoden, Archiv f. Naturg p. 142, 1853. 
3Fauna Ungarns Crustaceen. Verhandl. der zoologisch-botanischen Gesellschaft 
in Wien, 1858, p. 516. 
