468 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



gills at a density of 24° B. is one-eigliteenth 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 wonld have made the difference still greater, considering the 

 larger bulk of the body of Artemia salina compared with A. mueJil- 

 liausenii. 



It api)ears 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 densitj^, 

 Branchipus ferox Grube, and another species of Branchipus with hook- 

 like bent furcal lobes, which latter species I described as Branchipus 

 mediiis 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. Schaefferi) 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 

 postaMominal segments, with the last of these eight segments nearly 

 twice as long as the penultimate (Fig. 9c), w^hile Branchipus has oiine 

 such segments, of which the neighboring segments, by twos, show but a 

 small difference in length ; and, seconflly, 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- 

 al)dmnen of Artemia is homologotis with the tivo last segments of the post- 

 ahdomen in Branchipus, namely the eighth and ninth. 



In the progressive growth of several generations oX 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 (Figs. 10c and d), as in Branchipus. Branchipus, 

 however, in its youth and towards the end of its last 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 occnvTing 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 w^hich are of extraordinary 



