CHAP. II.] 



SEGMENTS OF ARTHROPODA. 



99 



number is a fair guide to the size of the fins, large fins for the most part havin» 

 many bristles and small fins having few. In the third column the range of this 

 number in several individuals is shewn, and for this purpose only adult females 

 bearing eggs in the ovisac are reckoned, as with sex and age there are changes in 

 respect of the number of bristles. 



ANALYSIS OF WATER FROM SIX LOCALITIES CONTAINING 



ARTE MIA SALINA. 



Catalogue Number 



Chlorine Cl 2 



Sulphuric 



anhydride S0 3 . . . 

 Carbonic 



anhydride C0 2 ... 



Lime CaO 



Magnesia MgO 



Soda and Potash 



Na 2 0, K,0 



Total" 



Oxygen equivalent 



to the Chlorine... 

 Total solids in 1000 



grams 



Sp. G. compared 



with Water at 20° 



XXIX. 



2-6950 



5-9105 



7-0125 

 •0311 

 •0384 



16-7471 

 32-4346 



•6082 



31-8264 



1-03074 



XIV. XLIII. 



24-8646 



13-3585 



•3185 



•2256 



3-3561 



27-4589 i 

 69-5822 



5-6112 



63-9710 



1-05196 



54-7793 



30-3797 



•3926 



•0678 



6-0367 



63-6088 

 155-2649 



12-3620 



142-9029 



1-11787 



XXVI. 



70-8130 



53-8150 



•2398 



•2266 



4-7514 



96-7906 

 226-6364 



15-9804 



210-6560 



1-17999 



XLIV. 



57-6653 



71-8775 



•3231 



•1466 



4-5115 



100-0803 

 234-6043 



13-0133 



221-5910 



1-19586 



XXIV. 



61-0830 



74-4463 



•2451 



•5175 



9-8394 



97-2084 

 243-3397 



13-7846 



229-5551 



1-20441 



These analyses were undertaken for me by Mr H. Robinson, of the Cambridge 

 University Chemical Laboratory, and my best thanks are due to him for the care 

 -with which he has conducted them. 



The table shews the great variability in the development of the tails and bristles. 

 In specimens from the same locality there is generally great difference, and even the 

 numbers on the two fins of the same individual are rarely the same. It will be seen 

 that on the whole the forms with few bristles came from waters of high specific 

 gravity, thus generally agreeing with Schmankewitsch's statement. This relation 

 to the salinity is not however very close, but Schmankewitsch never asserted 

 that it was. He fretmently refers to the existence of individuals with tails in several 

 conditions of degeneration in the same water, and especially (Z. f. w. Z., 1877, 

 p. 482) he expressly states that in the original locality of A. milhausenii he found 

 this form and with it several others intermediate between it and A. salina. 



It will also be seen in the Table, that the three samples, IV, XL and III stand 

 •out as having far more bristles than other samples from waters of ecpial specific 

 gravity. Each of these localities was exceptional, and all belong to one class. 

 Ill and IV were pools in the dry bed of a stream in the Kara Kum, near the Irghiz 

 river. They were close together, and must be joined in each spring. XL. was a 

 pool in a somewhat similar dried stream-bed, coming down to the lake Tulu Bai in 

 the district of Pavlodar. The conditions in these pools must be very different from 

 those of the large, shallow, permanent salt lakes from which the other samples 

 mostly came, and it is only fair to Schmankewitsch's case to remember that the 

 water in such pools must be almost fresh during the early part of each summer. 



On the whole, then, it seems satisfactorily shewn that the tailless form is con- 

 nected by intermediate stages with the fully-tailed A. salina, and that this transition 

 is at all events partly connected with the degrees of salinity of the water in which 

 it lives. Almost each locality has its own pattern of Arte mi a, which differs from 

 those of other localities in shades of colour, in average size, or in robustness, and 

 in the average number of spines on the swimming feet, but none of these differences 

 seem to be especially connected with the degree of salinity. 



7—2 



