478 GEOLOGICAL SURVEY OF THE TERRITORIES. 
specimens; but in the adult state, on their exterior terminus of the 
lobes, remain more or less short, sparsely placed bristles, the less the 
older the specimens are. As the smallest number of bristies, 1 found 
seven; so that at 6.97" length of a lobe its exterior margin was bristled 
only up to a distance of 1.5". As the highest number of bristles in 
mature specimens, I counted fifteen; so that at 6.87" length of a lobe its 
exterior margin was bristled up to a distance of 3.4™" from the tip of 
the lobe. 
To explain the formation of such a remarkable character as the miss- 
ing of bristles on the exterior margin of the furcal lobes in generations 
of Branchipus ferox inhabiting fresh-water ditches, we need only be 
reminded that these lobes are the longer the less dense the water is in 
which they live, and that in the real fresh-water generations of this 
species the furcal lobes are the largest. I have also observed that these 
lobes distend at a wide angle in swimming; the wider they distend the 
longer they are. In addition, the exterior margin of these lobes contin- 
ually cut the water, being therefore in a higher degree, subject to the 
mechanical influence of the water. Even if the pressure of the salt- 
water be higher then are the furcal lobes of the salt-water forms of this 
species much shorter, and, besides, we may say that the salt-lake gen- 
erations do not fully grow up; therefore, remaining provided with the 
principal characters of the young fresh-water forms. The fresh-water 
generations of Branchipus ferox have, amongst all European_species of 
Branchipus, the longest furcal lobes. 
The domestication ot several generations of this species in sait water 
of various concentration verifies also the effect of the surroundings. 
I therefore can see no necessity of admitting here an influence of nat- 
ural selection and to add new unknown factors to solve this problem. 
One of the most remarkable phenomena is the fact that in our shallow 
marine district so rich in salt-water basins (closed lakes and salt-water 
ditches), even in pure fresh water the typical fresh-water form of Bran- 
chipus ferox Chyzer does not occur, but only a form approximating in a 
certain degree those of the lowest generations of this species, inhabiting 
our salt-water ditches, connecting it with the Artemia; above all with 
the extreme race of Artemia salina (varietas a), which also lives in our 
salt-water ditches. This is not the only example of such an abberration 
of form. In the fresh waters of the neighborhood of Odessa we do not 
find the real Daphnia magna Leydig; however, one of its races occurs, 
representing an abberration toward Daphnia pulex Leydig! of a lower 
grade. The generations of our fresh-water Daphnia magna variety, 
distribute themselves also in a few salt ditches, where they form a still 
greater deviation from the typical form. In more saline ditches (ofabout 
3° Beaumé) occur such forms of Daphnia, bearing the characters of 
another, simultaneously reminding one of Daphnia magna varietas, D. 
pulex, and partly also of Daphnia reticulata and D. quadrangulata Leydig. 
I described this form under the name of Daphnia degeneraia? 
Regarding it as a degraded form of those ancestors, which gave origin 
to the existence of Daphnia magna and D. pulex, I actually convinced 
niyself in examining generations of Daphnia degenerata at ditterent 
seasons of the year and at various densities of the salt water, and also, 
by domesticating them, that it is a changed and degraded form of our 
1See my reports in the ‘‘Schriften” of the Neorussian Society of Naturalists, Vol. III, 
Part 2, pp. 196-216. 
2 Opus citatum, pp. 228-232. I have to add the following: The sensory antenna of 
the female of D. degenerata i is provided on its upper surface with the same bristle as 
occurs in D. magna. 
