chap, ii.] SEGMENTS OF ARTHHOPODA. 97 



var. a, 8 — 15, rarely more. Amongst specimens of var. a, as also among those of 

 the type, specimens maybe found having three, two, or even only one bristle on the 

 caudal fin. The second antennae of the male are less wide in var. a than in the 

 type, and the knobs on the inner border are rather larger than in the type. 



The variety b was found in pools of a concentration of 4° Beaume. It differs 

 from the type in having the post-abdomen shorter in proportion, though the whole 

 length is about the same. The number of bristles on the caudal fins is greater in 

 the variety. The second antenna? of the male are narrower in the variety than in 

 the type, and bear a tooth and a thickening of the skin internal to the rough knob- 

 like projections. But the most important difference characterizing var, b is the 

 appearance of transverse segmentation in the last (8th) post-abdominal segment. 

 This, according to Schmankewitsch, does not amount to an actual segmentation, 

 but is really a transverse annulation, which may be more or less conspicuous, and 

 suggests an appearance of segmentation. Schmankewitsch looks on this second 

 variety as a transitional form between Artemia and Branchipus, 



Before going further it may be remarked that Schmankewitsch gives no figures 

 of these varieties, except in so far as they are represented in the well-known Beriefl 

 of sketches of the caudal forks with varying numbers of bristles. No analysis of the 

 waters is given. 



It will be seen that two principal and distinct statements are made : 



(1) That A. milhausenii may be reared from A. salina by gradually raising the 

 concentration of the water. 



(2) That by diluting the water a division is produced in the last (8th) segment 

 of A. salina: that this is a character, or, as Schmankewitsch says, the chiei 

 character, of the genus Branchipus. 



First as to the relation of A. salina to A. milhausenii. The species milhausi nix 

 was made by G. Fischer de Waldheim 1 on spirit specimens sent to him, and the 

 absence of caudal fins and bristles was taken as the diagnostic character. Fischi 

 figures are very poor, and indeed are scarcely recognizable : they are also incorrect 

 in several points, giving for instance 12 pairs of swimming feet instead of 11. The 

 description is also very imperfect. In the course of this he speaks of the malt-. 

 saying that its second antennae are larger than those of the female, in which he 

 declares the second antennae may be sometimes absent. From Fischer's account it 

 is quite clear that his material was badly preserved, and indeed, as Schmankewitsch 

 says, specimens of these animals preserved with spirit only are of little use. 



In 1837 Rathke 2 gave a better figure of A. milhausenii l from the original 

 locality of Fischer's specimens. The tail, ending in two plain lobes, is shown. Tin- 

 male is not mentioned. The following analysis of the water is given : 



Potassium Sulphate 0*7453 

 Sodium Sulphate 2*4439 



Magnesium Chloride 7*5500 

 Calcium Chloride 0*2760 



Sodium Chloride 16*1200 



271352 



in 100 of the water. 



Other authors mention A. milhausenii, but there i-. so far as 1 am aware, no 

 special account of the male, or any material addition to the above. 



I will now give an abstract of such further evidence on this subject a- I have 

 been able to collect. 



In the course of a journey in Western Central Asia and Western Siberia 

 I collected samples of Branchiopods from a great variety of localities, of tl. 

 two consist of Branchipus ferox (Milne Edwards), one of Branchipus spinostu .Milne 

 Edwards), three of a species of Branchipus not dearly corresponding with any >p. . 

 of which a description is known to me, and the remainder of Artemia. All the sp* 

 of Branchipus collected are quite clearly defined both in the male and the female, 

 and have certainly nothing to do with the Artemia. Of the latter some preliminary 

 account may now be given, as the tacts bear on Schmankewitsch'a problem. 

 Omitting those which were badly preserved and those which do not contain adults, 

 there remain twenty-eight samples, satisfactorily preserved with corrosive Bublima 

 from as many localities. Of these, eight contain males, all of them having the 



1 Bull. Imp. Soc. Sat. Moscou, 1834, vxx. p. 152. 



2 Mem. Ac. Sci. P€t. t 1837. in. p. 395. 



B. 7 



