354 KANSAS UNIVERSITY SCIENCE BULLETIN. 



OBSERVATIONS ON THE SPERMATOGONIA. 



From a study of polar views of the equatorial plate the num- 

 ber of spermatogonial chromosomes was determined to be 

 twenty-one, and in no case was there observed a departure 

 from this characteristic number. The chromosomes in young 

 cells are larger than those in older cells and do not exhibit the 

 tendency to coalesce so readily. Consequently cells for study- 

 ing the number, form and behavior of the chromosomes were 

 comparatively few, although enough were found to leave no 

 doubt in the observer's mind as to the correctness of these 

 observations and their interpretation. Figures 1, 2, 3, 4, 5, 6, 

 7, 8, 9, 10, show polar views of the equatorial plate from 

 spermatogonial cells. Certain elements of the complex exhibit 

 constant and striking characteristics in size relationships. The 

 largest three chromosomes in each group are easily identified, 

 as are also the smallest two. The remaining members of the 

 group more nearly approximate each other in size, so no at- 

 tempt was made to homologize these in the several cells. 



The form of the chromosomes varies from spherical and el- 

 lipsoidal to kidney-shaped with variations in size and position. 

 The smallest two elements show the most striking differences 

 in these respects from the other members of the group. There 

 seems to be no fixed arrangement of the individual elements, 

 except that there is an evident pairing of twin chromosomes. 

 Sutton reported the presence of similar pairs in Brachystola 

 magna^- and his observations have been verified by other work- 

 ers in this laboratory on other species of the Orthoptera.f One 

 element of such a pair is considered to be of maternal origin 

 and the other of paternal origin. The tendency for equal ele- 

 ments to get together is very marked even in young cells, and 

 makes conspicuous the presence of an unpaired element, one of 

 the largest three chromosomes. Should its mate exist in the 

 cell it could not possibly be overlooked when even the smallest 

 elements are so prominent. Owing to uniformity in size, pre- 

 cisely which of the three is the unpaired element may be de- 

 cided upon only when two of them are unmistakably paired. 

 The smallest two elements show this tendency but rarely, their 

 behavior at this stage being consistent with subsequent irregii- 

 larities. 



* "Spermatogonial divisions of Brnchystola iiKK/na." Kansas University Quarterly, 

 vol. 9, No. 2. 1900. 



t The Chromo.some complex of SyrhuUi admirubilis. W. R. B. Robertson. Kansas Uni- 

 versity Science Bulletin, vol. IV, No. 13, 1908, 



