PACKAKB.] TEANSFOEMATIOX OF AETEMIA. 469 



size iu the male of Brancliipus spinosus. Such bristles we also find iu 

 Artemia in the same places and similarly distributed (Fig. 9fZ), only that 

 they do not arise out of a complex of dentate spines, bat out of the 

 middle of a complex of cuticular cells, which can scarcely be distiu- 

 tingnished from the surrounding; tissue (Fig-. 11). 



It is of some importance that in Artemia not onlj- near the end of 

 each segment do we find such circidarly placed bristles, but also in or a 

 little above the middle of the last long eighth postabdommal segment, 

 i. c, on that spot where the articulation ought to be, and where it is 

 actually found in Branchiinis, between the eighth and ninth segment, and 

 where in Artemia this articukuion after domestication of several gener- 

 ations in salt water of successive lower density, *. e., under such con- 

 ditions, is formed, which may be serviceable to progressive develop- 

 ment.^ 



Under the same conditions the complexes of cuticular cells just men- 

 tioned transform; out of their midst bristles develop by degrees in both 

 sexes of the domesticated Artemiae, into complexes of denticular spines, 

 as they are found in both sexes of Brancliipus. (Fig. 12.) 



These denticular spines are small and of equal size in both sexes of 

 Brancliipus ferox ; in the female of B. spinosus they are also smaS, but 

 iu the males of extraordinary size; in Brancliipus medius (described else- 

 where) they are large in both sexes, somewhat larger however in females 

 than in males. 



At the same time, in domesticating J.rfewm, all other characters change 

 progressively toward Brancliipus ; as, for instance, the length of the 

 furcal lobes, the number of their bristles, and so forth. 



After such results we unwillingly arrive at the conclusion that the 

 Artemia usually occurring in salt water of great density is nothing else 

 than a degraded form of Brancliipus under the influence of its surround- 

 ings, which latter form usually inhabits fresh water or salt water of low 

 density. 



On the other hand we have in Brancliipus a higher developed form of 

 Artemia^ which has transformed in a progressive direction. 



The cause of this may not only be the different concentration of the 

 water, but also its temperature. In nature Artcmice mostly inhabiting 

 salt lakes represent the summer forms, while Brancliipus, often populat- 

 ing dried-up pools, represents the spring or fall form. 



In domesticating, I observed that a high density of the water retains 

 the giowth and the development of specific characters of these animals, 

 while a simultaneous higher temperature evokes sexual maturity earlier 

 than the complete deve'opment of limbs ; higher temperature together 

 with higher density of the salt water also contribute to retrogradation 

 of forms and their degeneration. 



Of course, as I couviuced myself, a gradually increased density of the 

 salt water, even at a lower temperature, tends to degradation of forms; 

 for such a water, besides its mechanical influences upon the organism, 

 contains less oxygen than let^s saline water and much less than fresh 

 water, which plainly shows itself in artificially domesticating these 

 animals, and which ])oint I have already referred to. 



The following are the principal results of my investigations : 



1. In artificial domestication of several successive generations of Ar- 

 temia salina Milne Edw. in salt water of gradually increased density we 

 obtain a form identical with Artemia muelilhausenii M. Edw. 



2. Artemia salina M. Edw. is also apt in a state of nature after a 



1 See Plate II of the " Scliriften " of the third meeting of Russian Naturalists, Zoo- 

 logical Part. 



