1881.] Evolution of Branchiopod Crustaceans. 281 
tion, This exemplifies Dr. Dohrn’s theory! of the consecutive- 
ness of functions whose bearings concern one and the same 
organ, brought about by evolution. I refer to papers by Profes- 
sor Cope in the American Natura.ist, “ A review of the mod- 
ern doctrine of evolution,” etc. ! 
Professor Moritz Wagner's migration theory,? as well as Dr. 
Charles Darwin’s selection theory,? may be employed to explain 
the occurrence of the above-mentioned sets A, 2, and probably 
also C, 
First I must mention that, on keeping a number of Eubranchi- 
pus, male and female (the latter with ovaries filled and oviducts 
empty), together with a number of sets A and B, males and 
females (female in the same condition), during five days, I could 
never observe a single case of crossing; on the contrary, the two 
(red and white) avoided each other and only copulated among 
themselves. Now, as to set A,I consider them to be the first 
generation of Eubranchipus, brought along with mud into the 
little clay pool, by water birds, from the neighboring larger ponds.* 
The transparency of their bodies was produced by the chemico- 
physical influence’ of the little clay pool, and not by “ mimicry.” 
~ As the pool is an isolated one, there was no chance for the absorb- 
ing or obliterating influences of crossing with the original red 
Eubranchipus ; consequently the offspring of this new, colorless 
race, influenced by different factors, were liable to submit to still 
further evolutionary transformations which I believe have been 
réalized in set B: The animal gradually degenerated into a much 
smaller one with the above-mentioned characters. The factor that 
produced it was a conservative one, favoring the preservation of 
“Der Ursprung der Wirbelthiere und das Princip des Functionswechsels,’ 
Genealogische Skizzen yon Dr. Anton Dohrn. 1875. 
2«« Die Datwin’sche Theorie und das Migrationsgesetz der Organismen.” Von 
Dr. Moritz Wagner. 1868. The refutation of Wagner’s law of migration was 
attempted by my former tutor,.Professor Dr. Aug. Weismann (“ Ueber den Einfluss 
der Isolirung auf die Artbildung,” sae : sities Y a  saenelaeiae’ a — s 
paper he combined his theory with D a 
siderably deviate from each other as regards the sori i mechanical cause. 
also Kosmos, tv, April, 1880: « Ueber die Entstehung der Arten durch menisci 
Von Moritz Wagner. 
"On the Origin of Species by Means of Natural Selection.” 1859. _ 
*J. A. Ryder in Amer, Nat., XII, page 703. 
® See also papers by W. J. Schmankewitsch in Zeéé. foe qwiss. rats ig ee and 
1877. 
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