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THE AMERICAN NATURALIST [Vol. LVI 



discoveries of Walcott-^ in the Middle Cambrian of British 

 Columbia, are proven to reach back to the oldest fossili- 

 ferous beds (in Protocaris marshi Walcott to the Lower 

 Cambrian), Apus is the most remarkable and most often 

 cited form in paleontologic literature. The writer has 

 in a paper, now in press, shown that true Apus, identical 

 in form of carapace and " shell glands " has been found 

 in Permian beds of Oklahoma. It was before known from 

 the Triassic Buntsandstein of the Vogesian Mountains. 

 Its more than 70 pairs of gill-bearing feet and other 

 primitive characters have made it the model of compar- 

 ison for Paleozoic crustaceans, especially the trilobites. 

 The Lower Cambrian Protocaris marshi is so closely 

 allied to Apus that it was termed Apus marshi by Ber- 

 nard. There is hence no doubt of the immense age of 

 this type. 



Apus is now so parthenogenetical in its reproduction 

 that the males were not discovered until a hundred years 

 after the description of the first and best known species 

 {A. cancriformis Schatfer) ; and von Siebold repeatedly 

 investigated every member of a colony of Apus, once 

 over 5,000 in number, without finding a single male. At 

 other times he found one per cent, while in certain un- 

 known conditions (probably when food is scarce and life 

 generally unfavorable) the males may be developed in 

 crowds " (Geddes and Thompson, p. 189). Similar condi- 

 tions prevail in the brine-shrimp and the other branchio- 

 pods, cited above, as shown by Lereboullet and Nowikoff. 



Parthenogenesis is associated with other strange habits 

 in the three branchiopods, Apus cancriformis, Limnadia 

 hermanni, and Branchipus stagnalis, which occur together 

 in Europe. These creatures occur only after very wet 

 seasons in puddles, road-ditches and other small pools, 

 where their eggs have lain for decades in the dry mud, 

 exposed to heat and frost. They develop with amazing 



4 Walcott, Charles D., "Middle Cambrian Branchiopoda, Malacostraca, 

 Trilobita, and Merostomata," Smithsonian Miscellaneous Collections, Vol. 

 57, No. 6, 1912. 



