PACKARD. ] TRANSFORMATION OF ARTEMIA. AT5 
knobbed setz (Tast-borsten) are but little developed, being scarcely 
fifty times shorter than the antennz 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 tips of the 
male antenne 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 pale sensory 
threads situated on geniculated protuberances of the first posterior 
third section of the male antenne, 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 Daphnia 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-water individ- 
uals of this species have in their earlier stages a period during which they 
resemble in this, as well as in other respects, the mature forms of the salt 
lake. 
Besides the differences observed in the antenne of the salt-water 
generations of Daphnia rectirostris, our attention is called to the num- 
ber of slender “ gefiederten,” or, better, finely toothed spines, which 
occur on the lateral surface of the postabdomen of Daphnia rectirostris, 
running laterally seriatim and nearly parallel with the direction of the 
rectum. Leydig! 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. rectirostris on each 
side 11 to 13 of these spines or plates, 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 spincs at a certain age as the adult forms of the Chadschibai 
Lake, which demonstrates the retarded development of the latter. 
Furthermore, our fresh-water Daphniz (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 aumerous 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 5° Beaumé. 
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 temperature, than that fit for 
them in the very saline lake; that is, it wants a summer but no fall 
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, 
i. €., they approximate the fresh-water form. In so domesticating, 
1 Naturgeschichte der Daphniden, Leipzig, 1860, p. 175, Tab. X, 76. 
