PACKARD. 1 TEANSFOEMATION OF ARTEMIA. 475 



knobbed sette (Tast-borsten) are but little developed, being scarcely 

 fifty times shorter than the anteuuos themselves, while in the females of 

 the fresh water the same sensitive penicilli are moderately long, and 

 only six times shorter than the entire antenna. In the males, the sen- 

 sitive bacilli are also shorter than in those males inhabiting fresh water. 

 The small hooks situated near the sensitive bacilli on the ti})s of the 

 male antennce of fresh water are strongly curved with pointed tips, 

 while in the males of the Chadschibai Lake those hooks are shorter, 

 less curved, and with blunt tips. Of the two pointed i)ale sensory 

 threads situated on geniculated protuberances of the first posterior 

 third section of the male antenute, the posterior one is a little shorter 

 than the anterior thread, the latter coming out a little more in front. 

 These threads are in the males of JDaphnia rectirostris of the Chadschi- 

 bai Lake, not in a straight, but in a screw-like line. The distance 

 between one thread and the other is considerable, which character in 

 the fresh-water males is much'less prominent. The fresh-icater individ- 

 uals of this species have in their earlier stages a period during tvhich they 

 resemble in this, as ivell as in other respects, the mattire forms of the salt 

 lake. 



Besides the diiferences observed in the antennce of the salt-water 

 generations of Daphnia reetirostris, our attention is called to the num- 

 ber of slender " gefiederten," or, better, finely toothed spines, which 

 occur on the lateral surface of the postabdomeu of Daphnia rectirostris, 

 running laterally seriatim and nearly i)arallel with the direction of the 

 rectum. Ley dig ^ called them finely feathered spines, which I would 

 have called triangular, laterally finely dentate plates. However this 

 may be, we observe in our fresh-water forms of D. reetirosti^is on each 

 side 11 to 13 of these spines or i)lates, only 7 to 9 in the salt-lake form, 

 meaning here, as a matter of course, mature individuals only. In 

 younger specimens there are less spines than in the adults of the same 

 surroundings, and therefore the young fresh-water forms have the same 

 number of spines at a certain age as the adult forms of the Chadschibai 

 Lake, which demonstrates the retarded development of the latter. 

 Furthermore, our fresh-water Daphnise {D. rectirostris) are nearly color- 

 less, or of a slight yellowish color, while the same species in the salt 

 lake are of a reddish color. The so-called winter eggs of the former 

 have an ochreous or orange-colored yolk. Those of the latter are red 

 throughout. The bristles in general are less numerous in the salt-lake 

 form of the Daphnia than in the fresh- water form, and the average size 

 of body in the latter is also less than in the former, although the differ- 

 ence is but slight. 



The generations of D. rectirostris inhabiting our salt ditches repre- 

 sent in every respect a transitory form between the fresh-water form 

 and the salt-lake form, which lake has a higher density of the salt 

 water than the water in the salt ditches, where it fluctuates between 1° 

 and b'^ Beaume. 



In domesticating Daphnia rectirostris I also convinced myself that 

 the salt-lake form can also live at a lower concentration of the salt 

 water, only requiring herein a higher temj^/erature, than that fit for 

 them in tbe very saline lake; that is, it wants a summer but no iiill 

 temperature. In this less concentrated salt water the degradation of 

 individuals is considerably diminished with the generations, so that 

 they finally resemble the individuals of this species from salt ditches, 

 *. e., they approximate the fresh- water form. In so domesticating, 



1 Naturgeschiclitc der Dapliuiden, Leii)zig, 1860, p. 175, Tab. X, 76. 



