40 



NATURAL HISTORY OF ARTHROPODS. 



the adult. Both pairs of antennae occur, the second being modified in the males to 

 produce clasping organs. The locomotive feet are eleven in number, the only excep- 

 tion being nineteen in the Siberian genus, Polyartemia. The distinction between the 

 cephalo-thorax and abdomen is better marked than in the other families, and the abdo- 

 men bears two simple unjointed appendages. In many forms the front of the head is 

 prolonged into a peculiar appendage, which varies much in shape in the different 

 species. 



The genus Branchipus is, in the eastern parts of the United States, the most com- 

 mon of the Phyllopods, and the species known as _Z?. vernalis is one of the most familiar 

 fresh-water forms. Like others of the Phyllopoda, it inhabits temporary pools, those 

 formed by the melting snow in the early spring being favorite localities. Here they 

 may be found swimming on their backs in the most graceful manner imaginable, their 

 beautiful shades of red, flesh color, white, and greenish adding not a little to their 

 beauty. It is just these features which render it impossible for one to make any draw- 

 ing or illustration which will in any way compare with the originals. 



Artemia is a salt-water, or rather brine inhabiting, form, illustrated in North America, 

 according to the latest authority, by but a single species, Artemia gracilis. This is 

 found in immense numbers in Great Salt Lake and Mono Lake, and in brine pools 

 elsewhere in the country. They are frequently found in the salt water which is kept 

 in tubs on the railroad bridges across the heads of bays and similar places along the 



sea-coast. The food is apparently vegetable. 



In technical characters this and the next genus differ as 

 follows : Artemia has eight abdominal segments without ap- 

 pendages ; the second antennal claspers of the male have their 

 second joint flat and triangular, while the ovisac is short. In 

 JBranchinecta the abdomen has nine segments, the male claspers 

 are simple and cylindrical, and the ovisac is long and slender. 

 Under ordinary circumstances these would be considered as 

 of generic value, but what shall we say when we know the 

 results of the observations and experiments of the Russian 

 naturalist, Vladimir Schmankewitsch ? Condensed from his 

 account these were as follows: In 1871 the spring flood broke 

 down the barriers separating the two different lakes of the 

 salt-works near Odessa, diluting the water in the lower portion 

 to 8 Beaume, and also introducing into it a large number of 

 the brine shrimp, Artemia salina. After the restoration of 

 the embankment the water rapidly increased in density, until 

 in September, 1874, it reached 25 of Beaume's scale, and be- 

 gan to deposit salt. With this increase in density a gradual 

 change was noticed in the characters of the Artemice, until, 

 late in the summer of 1874, forms were produced which had 

 all the characters of a supposed distinct species, A. muehlhaus- 

 enii. The reverse experiment was then tried. A small quantity 

 of the water was gradually diluted, and, though conducted for 

 FIG. 54. a. Branchinecta only a few weeks, a change in the direction of A. salina was 



qrubei, male. b. Female, nat- . . , ... , 



iirai size. c. Artemia salina, very apparent. Led by these experiments he tried still others : 



Taking Artemia salina, which lives in brine of moderate 

 strength, he gradually diluted the water, and obtained as a result a form which is known 



