338 ANNALS NEW YORK ACADEMY OF SCIENCES 



Summary of Papers. 



Professor Osbom gave a summary of the valuable results of the expedi- 

 tion to the Fa\iim, Egjpt, in search of PaloEomasfodon and Arsinoitherium 

 which was illustrated by a fine series of stereopticon views. A detailed 

 account of the expedition has been published in Science. 



Professor Wilson, in his paper, said in brief: In striking contrast to 

 nearly all forms heretofore described, the genus Mefapedius presents a con- 

 siderable range of variation in the individual number of chromosomes, 

 though the number is constant in each individual. The following numbers 

 have thus far been observed in a total of 30 individuals (spermatogonia in 

 the males, ovarian cells in the females). M. terminalis, males 22, 23, females 



22, 25; M. femoraius, males 22, 23, 26, females 24, 26; M. granulosus, males 



23, 26, 27 (?), females 26. The variation is thus seen to be independent of 

 sex; and it is not a casual fluctuation within the individual, since the indi- 

 vidual number is constant and in the male is defuiitely correlated with the 

 number present in the maturation-divisions. Thus with 22, 23 or 26 sperm- 

 atogonial chromosomes the first spermatogonial division shows respectively 

 12, 13 or 16 chromosomes — a relation shown constantly and in a large 

 number of cells. Study of the conditions shown in the males leads to the con- 

 clusion that all individuals possess a fundamental or t\^e group of 22 chro- 

 mosomes that are always present and show the same general arrangement in 

 the first division. To these may be added in certain individuals one or more 

 "supernumerary chromosomes" which, like the idiochromosomes differ in 

 behavior from the others in failing to couple at the time of general synapsis, 

 dividing as univalents in the first division where they appear smaller than the 

 bivalents. Thus are explained the peculiar numerical relations above stated, 

 — e. g., 16 chromosomes in the first division include ten bivalents and six 

 univalents (two idiochromosomes and four supernumeraries). In the second 

 division the supernumeraries almost always unite with the idiochromosome- 

 bivalent to form a compound element; and the facts indicate that the indi- 

 vidual members of this complex may undergo an asymmetrical distribution 

 to the spermatozoa, which probably gives the explanation of the variations 

 observed in the somatic numbers of different individuals. The new proof 

 given by the facts of the genetic identity of the chromosomes, and their 

 possible bearing on certain phenomena of heredity were indicated. 



Dr. Hussakof , in his paper, said in abstract : The;leaves were collected 

 from a single tree during three successive summers beginning with 190-1, 

 and their variations in form statistically studied. During 1905 and 1906 

 "average samples" (about 500 leaves representing all parts of the tree) 

 were collected at intervals of about a month and systematically tabulated. 



