PACKAKD.] TEANSFOEMATION OF AETEMIA. 487 



a plienomenon is only explicable by the fact, that in a state of nature, on 

 the average, a lotcer temj^erature is, togetlier witli a higher density of the 

 salt icater than with A. salina, peculiar to the first variety of A. salina 

 (varietas a). The gill-sacs, 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 temiDerature. 



The first of these varieties of A. salina (varietas «.) corresponds amongst 

 our forms of Branchipus mostly with the species Branchipus s^nnosns 

 Milne-Edw., according to the relation of the gill-sac and posterior 

 branchial lobes and some other characters, together Avith the element 

 which it inhabits. Branchipus 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 princijDally 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- 

 I)eudages of the mature specimens of the stated variety of A. salina 

 (varietas a.), and altogether in younger age of the specimens of Branch- 

 ijius 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 matuie forms of the same species of Branchi])us. 

 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 aj)odous 

 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 apodons) segment of the abdomen in Artemia. In the 

 mature Branchipus spinosus the furca equals the section consisting of 

 the last two aj)odous segments. We obtain the following proportions : 



In the old specimens of In the young specimens of 



Branch, spinosus — Branch, spinosus — 



the giU-sacs amounted 



in leng-th the 40, in length the 24, 



in width the 118 in width the 61st 



part of the w^hole 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 {vnvietas 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 caijacity 



