468 GEOLOGICAL SURVEY OF THE TERRITORIES. 
gills at a density of 24° B. is one-eighteenth part; their width is the 
one-twenty-eighth part of the body length. 
In measuring the Artemia salina the furcal lobes were not counted in, 
which would have made the difference still greater, considering the 
larger bulk of the body of Artemia salina compared with A. muehl- 
hausenti. 
It appears that the species (Arten) of the genus Artemia are liable to 
undergo, also, progressive developments at a gradually lessened density 
of the salt water. The nature of those salt-water pools yields the con- 
ditions necessary for their progressive growth, which pools, after a 
number of years by continued washing of the briny soil, may turn into 
fresh-water pools. Indeed, Artemia salina inhabits, also, such salt-water 
pools in the neighborhood of the lake in which occurs, at a low density 
of the water, also Branchipus spinosus Grube; at a still lower density, 
Branchipus ferow Grube, and another species of Branchipus with hook- 
hike bent furcal lobes, which latter species I described as Branchipus 
medius in the “Schriften der dritten Versammlung russischer Natur- 
forscher.” 
In artificially domesticating Artemia salina in gradually diluted salt 
water I obtained a form with the characters of the genus Branchipus, 
(B. Schaeffert) which might be regarded as a new species of Branchipus. 
I had already occasion to discuss this point in the “Schriften” of the 
Russian Naturalists, third session, and in the “Schriften” of the Neo- 
russian Society of Naturalists (Vol. II, part 2), and again have to state 
as follows: 
The only two characters separating the genus Branchipus from the 
genus Artemia are the following: Firstly, that Artemia, inclusive of 
the genital segment (two segments together), possesses eight apodous 
postabdominal segments, with the last of these eight segments nearly 
twice as long as the penultimate (Fig. 9c), while Branchipus has nine 
such segments, of which the neighboring segments, by twos, show but a 
small difference in length; and, secondly, the existence of a physiologi- 
cal difference, parthenogenesis occurring in Artemia, which phenomenon 
has not yet been observed in Branchipus. This is a negative and ill- 
defined character. 
The first mark of distinction seems to be more important, but under- 
goes changes in Artemia under the influences of the surroundings, where 
the character of the genus Branchipus appears especially, than when 
several generations of Artemia are domesticated in gradually diluted 
salt water. 
I have convinced myself, that the last long eighth segment of the post- 
abdomen of Artemia is homologous with the two last segments of the post- 
abdomen in Branchipus, namely the eighth and ninth. 
In the progressive growth of several generations of Artemia in gradu- 
ally diluted salt water the last apodous eighth postabdominal segment 
of Artemia subdivides itself into two segments, whereby nine apodous 
segments are formed (Higs. 10¢e and d), as in Branchipus. Branchipus, 
however, in its youth and towards the end of its Jast larval state, has 
but eight abdominal segments, of which the last is also as long as in 
Artemia. Also without artificial domestication we can convince our- 
selves of the homology of the last eighth apodous segment of Artemia 
with the same two last apodous segments of Branchipus. 
In the species of Branchipus occurring in this region we find fine bristles 
distributed around the posterior end of each postabdominal segment, 
except in the last ninth segment. Every bristle arises from the mid- 
dle of a complex of small tooth-like spines which are of extraordinary 
