130 CARNEGIE INSTITUTION OF WASHINGTON. 



number of related species and in which it has been possible to trace 

 an evolution of morphological type. After this demonstration it will 

 be impossible to deny the "individuality of the chromosomes." Obvi- 

 ously it will be of great importance to compare the inheritance of traits 

 of which the determiners are carried in these dissimilar but closely 

 related germ-plasms. 



Mr. Metz further reports : 



"In addition to the Drosophila work, the study of the phenomena of chro- 

 mosome pairing and their significance has been followed up extensively. This 

 has involved the cytological study of at least 60 or 70 species of flies represent- 

 ing various families of the order (including the Drosophilidae). The essential 

 features of chromosome behavior have been found to agree in all, and to point 

 definitely to the conclusion that in all of them the chromosomes are permanent, 

 qualitatively different, individuals; and, further, that the two members of each 

 pair of chromosomes are homologous maternal and paternal elements which 

 remain associated with one another by reason of their qualitative similarity. To 

 my mind this latter forms one of the strongest cytological supports of the 

 chromosome theory of heredity, if the evidence for it is conclusive, as I believe 

 it to be. The report of this study is now nearly completed and will soon be 

 ready for publication. 



"In connection with the above study many interesting facts have been 

 observed with regard to the sex-chromosomes, and the general relation between 

 chromosome groups in the different families studied. It is astonishing what 

 a variety of conditions has been found as regards shape, size, and number of 

 chromosomes, presence or absence of chromatoid bodies, and other chromatic 

 structures, etc., in these various groups of flies. There has been no opportunity 

 to work these features out in detail, but there is material on hand for numerous 

 valuable studies. 



"One question upon which this material throws light has received definite 

 attention, however — namely, that of the maturation phenomena. Very little 

 is known about this question in the Diptera, yet it is one of especial importance 

 in connection with current theories of chromosome behavior, e. g., the "chias- 

 matype hypothesis," etc. Recently a supply of good material has been secured 

 from the Asilidse (robber flies) , which are most favorable for studying matura- 

 tion phenomena. This will be worked up and published as soon as possible, 

 but it will require many detailed and careful drawings, in addition to obser- 

 vational study, and just now more immediate work occupies all available 

 resources. 



"At present, especial attention is being paid to the study of oogenesis in 

 Drosophila ampelophila and to the work of determining the sex-chromosome 

 relations in the males of that species, because of their bearing upon genetic 

 data. Nothing very definite has resulted from this so far, however, although 

 a quantity of material has been studied. The problem is one of especial 

 difficulty as well as especial interest. 



"Throughout the year the principal problem attacked has been that of 

 hybridizing species of Drosophila possessing different chromosome groups. 

 A large amount of time has been devoted to this, but without success. The 

 experiments have now come to the stage in which it will be necessary either to 

 perfect a method for artificially fertilizing eggs of one species with sperm of 

 another or else to keep on getting additional species from localities hitherto not 

 worked until some are secured which will hybridize. Either of these methods 

 would give extremely important results if successful, but the latter would 



