3i6 RUDOLF RUEDEMANN 



rushed in, grabbed the strange creature, and ran back at top 

 speed to the high-school professor of biology who promptly took it 

 away declaring it to be the first he had ever seen alive! It is 

 told of Goethe that he had one brought to him while walking once 

 near Jena and that he became so excited over the weird animal 

 that he offered a thaler for the second, a guilder for the third 

 specimen, and so forth, but no other was found. Apus cancri- 

 formis grows within two weeks to full size which sometimes is nearly 

 five inches, lays an enormous number of eggs and dies.' Another 

 strange fact connected with this animal is that it produces the 

 eggs parthenogenetically. It was fully a hundred years after 

 the description of the species that any males were found. The 

 seventy pairs of appendages (among them fifty-two pairs of 

 abdominal feet with their gill-appendages) which give it its archaic 

 appearance are also connected with its life in very temporary 

 pools that lack the vegetation which oxygenates the water. 



All these facts show that the animal is adapted to most peculiar, 

 and it would seem also most precarious, conditions. It has been 

 therefore thought by some, as Salter and Packard,^ to be, together 

 with the rest of the Branchiopoda, highly specialized and com- 

 paratively modern. Its fossil record, however, contradicts this 

 conclusion, and from evidence, which the writer^ in a former paper 

 on arrested evolution has brought forward in regard to the factors 

 of persistence in animals, it follows that Apus belongs to that 

 class of persistent forms, that, at the height of their once vigorous 

 development, were able to penetrate into fields where weaker forms 

 could not follow them and it is precisely in these outskirts of the 

 arena of organic struggle that these types, after they were overtaken 

 by more rapidly developing forms, have managed to persist. This 

 would suggest that Apus had followed its present mode of life 

 through many periods, and the fossil evidence does not contradict 

 this suggestion; for the single Apus found in the Buntsandstein 

 may well have drifted in, together with the numerous remains of 

 landplants (Voltzia, etc.) found in that Triassic terrane. Regard- 

 ing the character of the Oklahoma deposit, from which our speci- 



' Weigand, 1913. 



2 See Schuchert, 1897, p. 675. ^ Ruedemann, 1918. 



