40 Experimental Zoology 
Ex periments with Flatfish 
There are some experiments made by Cunningham with 
young flatfish which also show the effect of an external agent, 
viz., light, on the development of color. Very young fish were 
put into aquaria lighted from below. As the young fish under- 
went their metamorphosis, the pigment gradually disappeared 
on one side, as it does under normal conditions, 7.e. as when 
they are lighted from above only. If, however, the fish are 
still illuminated from below, the pigment begins to come back 
again on the lower surface. The markings are similar in all 
respects to those on the upper side of the animal. 
The result shows that the lower side of flatfish in their natu- 
ral environment is white, because it is not exposed to light; but 
whether the result shows, as Cunningham believes, that the 
lower side has become white in the course of generations, be- 
cause it has been turned away from the light, is not shown 
conclusively by the experiment. 
Experiments with Crustaceans 
There are a few cases, in other groups, where it has been 
shown that external agents produce changes in form.  Bran- 
chippus ferox, inhabiting salt and fresh water, shows small 
differences in the length of the ovigerous sac, in the form of the 
segments of the body, in the length of the lobes that terminate 
the abdomen, and in the disposition of the abdominal bristles. 
Daphnia degenerata of salt water is only a degenerate variety 
of Daphnia magna of fresh water. 
A species related to Daphnia — Moina rectivoctris — oc- 
curs in one form in fresh water and in another in brackish. 
The two differ in general points of structure due to the indi- 
viduals becoming sexually mature before the final structural 
changes are completed. 
The oft-cited case of Artemia may also be mentioned here. 
Schmankewitsch has described the slow transformation of 
Artemia salina into A. milhausenii, as the lagoon in which the 
