96 MERISTIC VARIATION. [PART i. 



4. Branchipus and Artemia. As it has been alleged that variation may be pro- 

 duced in the segmentation of the abdomen of these animals by changes in the 

 waters in which they live, it is necessary here to give the facts on which this state- 

 ment rests. The further question of the relation of Artemia salina to A. mil- 

 hausenii is so closely connected with this subject, that though not strictly cognate, 

 some account of the evidence on this point also must be given. 



Some years ago Schmankewitsch 1 published certain papers on variations of 

 Artemia salina induced by changes in the salinity of the water in which the animals 

 lived. The statements there made excited a great deal of interest and have often 

 been repeated botb by scientific and popular writers. The facts have thus at times 

 been somewhat misrepresented, and so much exaggeration has crept in, that before 

 giving any further evidence it will be well to give Schmankewitsch's own account. 

 It is frequently asserted that Schmankewitsch observed the conversion of Branchipus 

 into Artemia and of Artemia salina into A. milhausenii following upon the pro- 

 gressive concentration of the waters of a salt lake. Strictly speaking however this is 

 not what was stated by Schmankewitsch. His story is briefly this: That the Bait 

 lagoon, Kuyalnik, was divided by a dam into an upper and a lower part; the waters 

 in the latter being saturated with salt, while the waters of the upper part were less 

 salt. By a spring flood in the year 1871 the waters of the upper part of the lake 

 swept over the dam and reduced the density of the lower waters to 8° Beaume 

 ( = about sp. g. 1-051), and in this water great numbers of A. salina then appeared, 

 presumably having been washed in from the upper part of the lake, or from the 

 neighbouring salt pools. After this the dam was made good, and the waters of the 

 lower lake by evaporation became more and more concentrated, being in the summer 

 of 1872 14° B (about sp. g. 1-103) ; in 1873, 18° B (about sp. g. 1-135); in August 1874, 

 23-5° B (about sp. g. 1-177) and later in that year the salt began to crystallize out. 

 In 1871 the Artemia had caudal fins of good size, bearing 8 to 12, rarely 1 5, l'Hstles, 

 but with the progressive concentration of the water the generations of Artemia 

 progressively degenerated, until at the end of the summer of 1871 a large part of 

 them had no caudal fins, thus presenting the character of A. miliums, mi Fischer 

 and Milne Edw. The successive stages of the diminution of the tail-fins and of the 

 numbers of the bristles are Bhewn in the figures, with which all are now familiar. 



A similar series was produced experimentally by gradual concentration of water, 

 leading to the extreme form resembling A. milhausenii. It was found also that if 

 the animals without caudal tins were kept in water which was gradually diluted, 

 after some weeks a pair of conical prominences, each bearing a single bristle, ap- 

 peared at the end of the abdomen. 



It is further stated that the branchial plates- of the animals living in the more 

 highly concentrated water were materially larger than those of animals living in 

 water of a less concentration. 



Schmankewitsch next goes on to say that by artificially breeding Artemia salina 

 in more and more diluted salt water he obtained a form having the characters of 

 Si ii a i Fi'.n's genus Branchipus, and that he considers this form as a new species of 

 Branchipus. He explains this statement thus: In the normal Artemia, the last 

 Begment of the post-abdomen is about twice as long as each of the other segments, 

 while the corresponding part in Branchipus is divided into two segments. He states 

 that in his opinion the condition of the last segment of the post-abdomen consti- 

 tutes the essential difference between Artemia and Branchipus, and that such 

 division of the last segment occurred in the third generation of the form produced 

 by him from Artemia by progressive dilution of the water. A second distinction 

 between the genera is found in the fact that Artemia is reproduced partheno- 

 genetically, while Branchipus is not known to be so reproduced. As to the 

 condition of his new form in this respect, Schmankewitsch had no evidence. 



In a subsequent paper, '/.. f, w. '/.. . 1877, further particulars are given, re- 

 specting especially the natural varieties of A. salina. Of these he distinguishes two, 

 var. a and var. b. The first of these i^ distinguished by its greater size (8 lines 

 instead of 6 lines, the average for the type) and by the greater length of the post- 

 abdomen. In the type the bristles on each caudal fin are generally 8 — 12, and in 



1 Z. f. w. Z., xxv., 1875, 2, p. 103 and xxix., 1*77. p. 42«J ; also in several 

 Russian publications, to which references will be found /. <•. 



Upon this point a good deal of interesting evidence is given in Schmanke- 

 witsch's papers, but as it does not bear immediately on the question of the specific 

 differences, it has not been introduced here. 



