G. GENERAL NATURAL HISTORY AND ZOOLOGY. 357 



mal, whose remains have been found in the post-Tertiary beds 

 of Buenos Ayres. His observations led him to coincide with 

 the view of Owen that Toxodon represents a distinct order 

 of mammals. Professor Cope recently pointed out the small 

 size of the brain in Symborodon, from the Miocene strata of 

 the Plains, showing that the greater part of the skull was 

 occupied by immense air-chambers. Professor Marsh, of 

 Yale College, has since compared the brain cavities of vari- 

 ous genera of the American Eocene and Pliocene periods 

 with existing forms, and finds those of the first-named epoch 

 to be exceedingly small, and that there is a steady increase 

 in size in the subsequent periods. Thus the brain in the gi- 

 gantic Uintatheriitm, of the Eocene, is little larger than that of 

 some reptiles. In the lines of the rhinoceros, tapir, and horse 

 a regular increase in size from such beginnings can be traced. 



DIMORPHISM IX CERTAIN BUTTERFLIES. 



Some species of butterflies of the well-known genus Grapta 

 have been found by Mr. "W. H. Edwards to be dimorphic 

 forms. By the simple experiment of tying up a Grapta 

 dry as in a bag at the end of a branch of its food-plant, it 

 laid a batch of eggs from which resulted a large number of 

 G. comma and six G. dryas. He now gives in the Cana- 

 dian Entomologist the results of an experiment made with 

 Grapta comma, the converse of that made in 1873 with dry- 

 as. On the 10th of May last he took a female, true comma, 

 and tied it up to a branch of hop-vine. She laid in the bag 

 some forty eggs, from which hatched thirty-nine caterpillars. 

 Most of them in due time reached the chrysalis state; and 

 between the 10th and 15th of June there emerged thirty-four 

 butterflies, every one a Dryas. 



ANOTHER LINK CONNECTING BIRDS AND REPTILES. 



One of the most important papers read at the Hartford 

 Meeting of the American Association for the Advancement 

 of Science was presented by Professor E. j8. Morse. In it he 

 points out an additional link connecting the birds and rep- 

 tiles. The astralagus (one of the bones of the ankle) co-ossi- 

 fies early with the end of the tibia, and this "process," as it 

 has been erroneously called, ascends as a spur from the upper 

 side of the astralagus in front of the tibia. In certain ex- 



