TERTIARY ANIMALS. 



515 



Vanessa Pluto. 



Heer has described 500 species. Mammalian remains and fishes are 

 also found in them. 



It is interesting to inquire into the conditions under which these 

 strata were formed and filled with these remains. On Lake Superior, 

 at Eagle Harbor, in the 

 summer of 1844, we 

 saw the white sands of 

 the beach blackened 

 with the bodies of in- 

 sects of many species, 

 but mostly beetles cast 

 ashore. As many spe- 

 cies were here collected 

 in a few days, by Dr. 

 J. L. Le Conte, as could 

 have been collected in 

 as many months in any other place. The insects seem to have flown 

 over the surface of the lake ; to have been beaten down by winds and 

 drowned, and then slowly carried shoreward and accumulated in this 

 harbor, and finally cast ashore by winds and waves. Doubtless, at 

 (Eningen, in Miocene times, there was an extensive lake surrounded by 

 dense forests ; and the insects drowned in its waters, and the leaves 

 strewed by winds on its surface, were cast ashore by its waves. Heer 

 believes also that carbonic-acid emissions helped to destroy, and de- 

 posits of carbonate of lime to preserve, the insects. Over five hundred 

 of the (Eningen insects were beetles. 



Among the insects found at (Eningen, Switzerland, and Eadoboj, 

 Croatia, are a great many ants (Fig. 877). In all Europe there are 

 now about fifty species of ants. Heer found in the Miocene of (Enin- 

 gen and Radoboj more than 100 species* And, what is very remark- 

 able, nearly all are winged ants. Ants of the present day are male, 

 female, and neuter. The males are winged throughout life, and never 

 live in the nests, but soon perish. The females are also winged until 

 they are fertilized ; then they drop their wings and live in communi- 

 ties in a wingless condition ever afterward. The neuters are always 

 wingless, and therefore always live in nests or in communities. It is 

 probable that ants at first were only winged males and females, living 

 in the open air like other insects. The wingless condition and the neu- 

 tral condition are both connected with their peculiar social habits and 

 instincts, and have been gradually developed along with the develop- 

 ment of their habits and instincts. It is probable that all these remark- 

 able peculiarities, viz., the wingless condition, the neutral condition, the 



* Pouchet, Popular Science Monthly, June, 1S73. 



