m'clung: cytology and taxonomy. 203 



tetrads. This is a generic character, one of those that serve to 

 distinguish the group that taxonomists have called Hesperotet- 

 tix from other members of the family Acrididse. With my 

 present knowledge I would feel safe, if I found an acridian 

 cell containing such an element, in ascribing its source to the 

 genus Hesperotettix. I should have as little doubt regarding 

 its distinctive character as I should have regarding that of the 

 animal from which it came. So far as I have been able to see, 

 there is no other character of the cell that would distinguish 

 this genus from the remaining ones of the Acrididse. 



Then it became necessary to see if there were peculiarities 

 that bore any constant relation to body characters of specific 

 value. It was most interesting to find that the multiple chro- 

 mosome, so constant a generic character, should exhibit just 

 as constantly minor modifications of size and proportion in the 

 different species. This particular chromatic element there- 

 fore signifies to my mind as definite an integration of substance 

 as does the adult animal which contained it. The differences 

 between the same element in the three forms of Hesperotettix 

 studied are just as specific as any that might be chosen from 

 somatic characters. It would perhaps be well to say that I 

 have made most careful comparisons in the size of these chro- 

 mosomes, and it is very remarkable to find the extremely close 

 concordance that exists within the species. If this is true of 

 the fixed material which has been subjected to all the violent 

 processes incident to the preparation of slides, how much more 

 true it must be for the living object. 



There are thus within the germ-cells of these animals certain 

 structures that show specific, generic, and family characters in 

 just as pronounced a manner as do the completed organisms 

 wherein they are found. It is therefore desirable to know 

 what corroboration we have from the study of other organisms 

 for our belief in the great importance of the chromosomes. I 

 would ask you, therefore, to review with me very briefly a series 

 of facts which cytology, normal and experimental, has brought 

 forth in support of the idea that the chromatin is the guiding 

 and controlling element in development, and that the chromo- 

 somes represent definite centers of influence. 



In the first place, organisms without chromatin do not exist, 

 and when the nucleus is removed from an individual the nor- 

 mal functions cease. The necessity of the chromatin in the 

 economy of the cell is thus proved. Next we may note that the 



