404 ANNALS NEW YORK ACADEMY OF SCIENCES 



Summary of Papers. 



Dr. Davenport said in abstract : Professor Plate has described, in the 

 Archiv. f. Rassen- und Gesellschaftsbiol., Bd. IV, the different forms of 

 a genus of land snails (Cerion) from the Bahama Islands; and declares 

 that the Cerions of the north coast of New Providence constitute the best 

 known and most known and most manifold example of such a morpho- 

 logic-geographic "form chain" as the Sarasins describe. Going from the 

 west to the east end of the island, "regular and definitely directed 

 changes" are said to occur "conditioned by the amount of precipitation 

 together with an inner factor — a high responsiveness of the protoplasm." 

 In January, 1910, I collected shells in New Providence from the localities 

 specified by Plate and from several others. I am now attempting to 

 breed them. Meanwhile the evidence seems opposed to Plate's view, since 

 the "western" type is foimd at various localities in the east alongside of 

 the eastern type. The facts seem to accord better with the view of the 

 immigration into the eastern end of New Providence of snails having the 

 characteristics of Cerions from the Eleuthera Island (an immigration 

 facilitated by geographic conditions) and by the formation of varied 

 combinations of characters and pseudo-blends by hybridization. 



Dr. Davenport's paper was illustrated with specimens and diagrams. 



Mr. Gregory said in abstract : Reichert's conclusion that the incus and 

 malleus of mammals represent the vestigial and metamorphosed jaw ele- 

 ments of lower vertebrates, together with the opposing view that these 

 ossicles in the mammalia have been derived directly from the supra- and 

 extra-stapedial cartilages of reptiles, were considered. Exception was 

 taken to Dr. Broom's form of the latter theory, which took the auditory 

 ossicles of the crocodile as a theoretical starting point. All the bones sur- 

 rounding these elements in the crocodile had evidently undergone certain 

 peculiar specializations and it would be surprising if the auditory ossicles 

 themselves had not also suffered considerable modification in the endeavor 

 to evolve an improved auditory apparatus. The resemblances in the 

 ossicles between crocidile and mammal may therefore be due chiefly to 

 convergent evolution. The modern upholders of the incus-quadrate, mal- 

 leus-articular theory demand for the ancestral mammal a freely movable 

 quadrate, similar to that of the lizard ; but this was because they seem to 

 push too far the biogenetic law. The incus or supposed homologue of the 

 quadrate at present appears in the embryo as a freely movable bone, but 

 this does not prove that it has always been freely movable. These inves- 

 tigators had passed by the theridonts of the Permian and Triassic because 

 in these reptiles the quadrate was fixed at its upper end; but a slight 



