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 bristles, 1 found 

 seven ; so that at 6.9""" 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 6.8""" length of a lobe its 

 exterior margin was bristled ui) 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 BraivMpus 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, w^e may say that the salt-lake gen- 

 erations do not fully grow uj); therefore, remaining provided with the 

 principal characters of the young fresh-water forms. The fresh- water 

 generations of BrancMpus ferox have, amongst all European^species of 

 Brauchi])us, the longest furcal lobes. 



The domestication ot several generations of this species in sa^t water 

 of various concentration verities also the eifect of the surroundings. 



I therefore can see no necessity of admitting here an iutiaence 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- 

 cMpus 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 Ba-plmia magna hey dig; however, one of its races occurs, 

 representing an abberration toward JDaphnia pulex Leydig^ of a lower 

 grade. The generations of our fresh-water Baphnia. 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 (of about 

 3° Beaume) occur such forms of Daphnia, bearing the characters of 

 another, simultaneously reminding one of Baphnia magna varietas, B. 

 pulcx, and partly also of Baphnia reticulata and />. quadrangulata Leydig. 

 I described this form under the name of Baphnia degenerata^ 



Eegarding it as a degraded form of those ancestors, which gave origin 

 to the existence of Baphnia magna and B. pulex^ I actually convinced 

 myself in examining generations of Baphnia degenerata at different 

 seasons of the year and at various densities of tlie salt water, and also, 

 by domesticating them, that it is a changed and degraded form of our 



1 See my reports iu the ' ' Scliriften " of tbe Neorussian Society of Natiiralists, Vol. Ill, 

 Part 2, pp. 196-216. 



2 Opns citatum, pp. 228-232. I have to add the folIowiDg: The sensory antenna of 

 the female of I), degenerata is provided ou its upper surface with the same bristle as 

 occurs in D. magna. 



