312 



SCIENCE. 



[N. S. Vol. XI. No. 269. 



yet in form for publication. The problems dis- 

 cussed — the origin of the solar system, the 

 source of the earth's heat, the earth's physiog- 

 nomy, its atmosphere, etc., had all been in- 

 volved in an attempt to frame an adequate work- 

 ing hypothesis to explain the glacial periods. 



It was shown that all the hypotheses thus far 

 advanced to explain the glacial periods fail of 

 correspondence with the known facts of geology, 

 particularly the discovery of glacial periods 

 earlier than that of the Quaternary. The 

 kinetic theory of gases applied to the atmos- 

 pheres of the planets was found to invalidate 

 the La Placian theory of the universe as well 

 as the later theory of meteoric swarms. The 

 atmosphere being the blanket of the earth 

 the explanation of the earth's warm and cold 

 periods was sought in the variation of the 

 amount of carbon dioxide contained, which 

 would materially affect screening or blanketing 

 capacity. Alternate depletion and repletion 

 of the carbon dioxide of the atmosphere might 

 be caused by the variation in the size of land 

 areas and the consequent variation in the car- 

 bonation of rocks, and by the separation of car- 

 bonates from the littoral portions of the seas. 

 Mr. Chamberlin discussed a theory of the origin 

 of the earth by the slow accretion of solid mat- 

 ter from without, a theory in contrast with that 

 of La Place, in that instead of beginning with 

 an enormously heavy atmosphere, on his theory 

 an atmosphere could not exist until the earth 

 was about one-tenth grown, and would then be 

 extremely attenuated to increase in density 

 with the enlargement of the planet. The ex- 

 ceeding difficulty of securing data for calcula- 

 tion in this field was emphasized, as was the 

 necessity of submitting not one but a number 

 of working hypotheses to the most searching 

 of tests. ^jj jj HOBBS. 



ZOOLOGICAL CLUB, UNIVERSITY OF CHICAGO, 

 MEETINGS OF DECEMBEE, 1899. 



The session of December 15th was devoted 

 to a paper by Mr. M. F. Guj'er on ' Spermato- 

 genesis of Hybrid Pigeons.' " In the sperma- 

 togenesis of hybrid pigeons several abnormal- 

 ities are manifested. These may be classified 

 conveniently under three heads : (1) abnormal- 

 ities in the structure of the spermatozoa ; (2) 



abnormalities in mitoses ; (3) degeneration of 

 the germinal cells. Abnormalities in the sperma- 

 tozoan structure were present in sterile hybrids, 

 the most noticeable feature being a varicosity 

 or swelling about the middle of the head. In 

 tracing the development of the spermatozoa, 

 this curious modification was found to be due 

 apparently to a lack of development of the 

 head ; the nucleus did not elongate completely 

 as in normal spermatogenesis. Abnormalities 

 in mitosis were marked in both fertile and 

 sterile hybrids. Large numbers of multipolar 

 spindles were present. These were usually of 

 the tripolar type. Occasionally two distinct 

 and separate spindles occurred in one cell. 

 The spermatocytes of the first order were the 

 the cells that showed this phenomenon to the 

 greatest extent. In the normal pigeon the 

 chromosomes in the spermatogonia are sixteen 

 in number and in the primary spermatocyte 

 eight. The latter are laid down in rings and 

 each is evidently double. On the spermato- 

 gonia of the hybrid there were sixteen chromo- 

 somes and in the primary spermatocytes often 

 more than eight. In the latter there may be 

 several of the large double type and a number 

 of smaller rings, or sixteen small ring chromo- 

 somes may occur. If sixteen rings were pres- 

 ent they were usually located on two separate 

 spindles, eight to each spindle. Another pecu- 

 liarity in the mitosis was the frequent inequality 

 in the division of the chromosomes, in some 

 instances only about a fourth of a chromosome 

 going to one pole. It is a well known fact that 

 the descendants of hybrids are remarkably 

 variable, hence the possibility that this irregu- 

 larity in chromatin distribution of the parent 

 germ cell and the variability of the offspring 

 may be connected in some way immediately 

 suggests itself. As for the degeneration of 

 the germ cells, this phenomenon was observed in 

 sterile birds onlj'." 



At the meeting of December 20th, Dr. E. S. 

 Riggs, of the Field Columbian Museum, con- 

 tributed an illustrated lecture, ' The Fossil 

 Mammals of North America.' A large number 

 of lantern slides were exhibited ; among them 

 many reproductions in color of the restora- 

 tions of fossil mammals executed by BIr. Knight. 

 C. M. Child. 



