PACKARD. ] TRANSFORMATION OF ARTEMIA. 469 
size in the male of Branchipus spinosus. Such bristles we also find in 
Artemia in the same places and similarly distributed (Fig. 9d), only that 
they do not arise out of a complex of dentate spines, but out of the 
middle of a complex of cuticular cells, which can searcely be distin- 
tinguished from the surrounding tissue (Fig. 11). 
It is of some importance that in Artemia not only near the end of 
each segment do we find such circularly placed bristles, but also in or a 
little above the middle of the last long eighth postabdominal segment, 
t. €., on that spot where the articulation ought to be, and where it is 
actually found in Branchipus, between the eighth and ninth segment, and 
where in Artemia this articulation after domestication of several gener- 
ations in salt water of successive lower density, 7. 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 Artemiz, into complexes of denticular spines, 
as they. are found in both sexes of Branchipus. (Fig. 12.) 
These denticular spines are small and of equal size in both sexes of 
Branchipus ferox ; 1a the female of B. spinosus they are also swak, but 
in the males of extraordinary size; in Branchipus medius (described else- 
where) they are large in both sexes, somewhat larger however in females 
than in males. 
At the same time, in domesticating Artemia, all other characters change 
progressively toward Branchipus; as, for instance, the length of the 
furcval 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 Branchipus 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 Branchipus 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 Artemie mostly inhabiting 
salt lakes represent the summer forms, while Branchipus, 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 growth and the development of specific characters of these animals, 
while a simultaneous higher temperature evokes sexual maturity earlier 
than the complete development 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 convinced 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 less saline water and much less than fresh 
water, which plainly shows itself in artificially domesticating these 
animals, and which point 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 muehlhausenii M. Edw. 
2. Artemia salina M. Edw. is also apt in a state of nature after a 
1 See Plate II of the “Schriften” of the third meeting of Russian Naturalists, Zoo- 
logical Part. 
