PACKARD.] TRANSFORMATION OF ARTEMIA. 487 
a phenomenon is only explicable by the fact, that in a state of nature, on 
the average, a lower temperature is, together with a higher density of the 
salt water than with A. salina, peculiar to the first variety of A. salina 
(varietas a). The gill-saes, as special organs of respiration, must become 
smaller by a lower temperature, whilst the posterior branchial lobes, as 
the auxiliary organs of locomotion, must enlarge by the greater density 
of the water dependant on the lower temperature and the higher con- 
centration. But since the density of the salt water depends more on 
its concentration than on temperature, it is obvious why, by domestica- 
tion of Artemia, we observe more changes in the posterior branchial 
lobes by the concentration of the salt water than by temperature. 
The first of these varieties of A. salina (varietas a.) corresponds amongst 
our forms of Branchipus mostly with the species Branchipus spinosus 
Milne-Edw., according to the relation of the gill-sac and posterior 
branchial lobes and some other characters, together with the element 
which it inhabits. Brunchipus spinosus is characterized among our 
forms of Branchipus in a similar manner as the first variety of A. salina, 
and A. salina by small gill-sacs and large posterior branchial lobes, 
only herein Branchipus spinosus is the difference in size of these append- 
ages considerably larger. Such a phenomenon also fully corresponds 
with that element which Branchipus spinosus among our salt-water forms 
of Branchipus principally inhabits. It lives, in comparison with our 
other Branchipus forms, in a lower temperature, but at a higher con- 
centration of the water. Especially in younger age and at a certain 
time the gill-sacs and posterior branchial lobes much resemble the ap- 
pendages of the mature specimens of the stated variety of A. salina 
(varietas a.), aud altogether in younger age of the specimens of Branch- 
ipus there is a certain period when their leg-appendages in measure- 
ments more approach the appendages of the mature forms of Artemia 
than the appendages of mature forms of the same species of Branchipus. 
For comparison we take mature individuals of Branchipus spinosus and 
young individuals of this species, some time after they quitted their 
larval state, when the section between the eighth and ninth apodous 
segments of the abdomen has scarcely just been formed, and the furca 
is still two or two and a half times shorter than the section consisting 
of the two last segments of the abdomen, and which is homologous with 
the last (eighth apodous) segment of the abdomen in Artemia. In the 
mature Branchipus spinosus the furca equals the section consisting of 
the last two apodous segments. We obtain the following proportions: 
In the old specimens of In the young specimens of 
Branch. spinosus— Branch. spinosus— 
the gill-sacs amounted 
in length the 40, in length the 24, 
in width the 118 in width the 61st 
part of the whole body-length; 
the posterior branchial lobes amounted 
in length the 19, in length the 16, 
in width the 37 in width the 28th 
part of the whole body-length. 
The first variety of A. salina (varietas a.) is in relation to this, 
especially concerning the gill-sacs, between the species A. salina and 
the young specimens of Branchipus spinosus. I only kept the figure 
of the measurement of varietas a. of A. salina at such a salt capacity 
