214 KANSAS UNIVERSITY SCIENCE BULLETIN. 



niteness in the grasshoppers. We do not yet know how much 

 difference there may be in the organization of the various 

 chromosomes of a complex nor how variable in importance they 

 may be. We know that eggs differ much in the extent of their 

 organization, so that their potencies are entirely different; and 

 since the chromosomes represent a part of this organization 

 they also may vary in some forms. There may also be more 

 than the duplicate set of chromosomes present, which would 

 presumably do no more than bring about greater variation or 

 minor differences in the distribution of characters. 



Taxonomy has sought to determine the true relationship be- 

 tween animals and to divine the lines of their descent. As 

 criteria they have used, in the main, structural peculiarities, 

 and these have been considered of different values, depending 

 upon the number and variety of forms to which they are com- 

 mon. We speak in this way of family, generic and specific 

 characters. For instance, in the Orthoptera we distinguish 

 the family AcrididsR, which has as recognition characters 

 strongly developed jumping legs, vertical head, short antennae, 

 three ocelli, three- jointed tarsi, auditory organs on the basal 

 segment of the abdomen, etc. An examination of these char- 

 acters will show that it is not the presence of any peculiar 

 structure that distinguishes this group of Orthoptera from 

 other Orthoptera, but it is the nature and extent of structural 

 development that is distinctive. All insects have, for instance, 

 a third pair of legs, a pair of antennae, a head, etc., but in the 

 Amididas it is the particular proportion of the third pair of 

 legs, the length of the antennae, and the position of the head 

 with reference to the thorax that marks off this group from 

 others. It is the entire organization of the acridian body that 

 differs from representatives of other orthopteran families, and 

 these features of external structure that taxonomists have se- 

 lected are merely very striking ones used for diagnostic pur- 

 poses. 



Not a cell in the body of an acridian is like that of a locustid, 

 nor are any of the organs similar. The structure of the testis, 

 for instance, is so dissimilar that a glance at a section through 

 a low power of the microscope is sufficient to distinguish the 

 source of the preparation without counting the chromosomes. 

 I have therefore come to the conclusion that for accurate, sys- 

 tematic work, not only will the external anatomy have to be 

 studied but also the internal. Ordinarily, the correlation of 



