METAZOA CRUSTACEA. 329 



the water in which Artemia salina M. Edw. was living, it 

 was transformed into another species, Artemia ?niihl- 

 hausmi M. Edw. Again, this brine was diluted and 

 Artemia miihlhauseni was changed back to Artemia 

 salina. 1 In this way it has been proved that not only 

 one species can be converted into another species, but 

 that the same is true of genera. 



Figures of the two animals would not bring out these 

 changes since they take place in the details of structure 

 (such as the number of the abdominal segments and the 

 bristles and knobs of the terminal abdominal append- 

 ages), but they are clearly represented in PL 809, figs. 

 1-8. The long terminal segment of the abdomen of 

 Artemia salina is seen in fig. i ; this becomes divided 

 into two segments (fig. 2), as in the abdomen of Branchi- 

 pus. Figs. 3-8 show the gradual reduction of the bristles 

 of Artemia salina (fig. 3) to the knobs of Artemia miihl- 

 hauseni (fig. 8). 



The American species of Artemia (A. gracilis Verrill) 

 (PI. 8 10, fig. i) lives in Great Salt Lake, and the New Eng- 

 land species of Branchipus {B. vernalis Verrill) (fig. 2), is 

 often found during the spring and autumn in ponds that 

 dry up in the summer time. They are graceful little 

 creatures that swim on their backs with great rapidity, 

 their light colored bodies contrasting prettily with their 

 brightly tinted locomotor organs which combine the 

 function of feet and gills. 



Apus lucanus Packard (No. 811) is a fresh-water spe- 

 cialized Phyllopod. The anterior part of the body is 

 covered with a large carapace which, however, is not 

 soldered to the thoracic region. When this carapace is 

 removed the segmented body is exposed beneath. It 

 consists in this genus of not less than sixty-nine seg- 

 ments. 



1 For further information see Zeitschr. f. wiss. Zool., XXV, 

 Suppi., 1875; also I2th Ann. Rep. U. S. Geol. and Geogr. Surv., 

 1878, part i, pp. 466-514. 



