ig4 McCLUNG. [Vol. II. 



the accessory chromosome of XipJiidium in the earlier stages 

 of its formation. Again, in Figs. 40^7, ^ob, 41a, and 41^ appears 

 a nuclear element, marked "x," that is clearly to be distinguished 

 from the other chromatic structures. The same element is traced 

 through later stages, but its ultimate fate is not indicated. 



Resembling the retarded separation of the accessory chromo- 

 some in the cells of Xiphidiiivi, shown in Figs. 5 and 6, is that 

 of a pair of chromosomes shown by Henking in his Figs. 55- 

 58. These appearances certainly indicate a resemblance between 

 insect seminal cells that is worthy of attention. 



The figures accompanying this paper are diagrammatic, and 

 are intended merely to show the one nuclear element in the 

 various stages of its transformations. More detailed drawings 

 will accompany a subsequent paper, in which will be recorded 

 a general history of the male reproductive cells of XiphidiuTn. 



Technical Details. 



The material employed in the investigation was collected in 

 Chicago during the months of July and August. Nymphs having 

 the wings but scarcely developed exhibited the most complete 

 series of reproductive cells. To fix the tissues, Flemming's 

 fluid, Hermann's fluid, corrosive-acetic mixture, platinic chloride 

 solution, and chromic acid combined with formalin were em- 

 ployed. Osmic acid mixtures gave the best results, and were 

 finally used to the exclusion of all other fixing agents. 



Sections cut 2^ /a and 5/x thick were fastened to the slide 

 by the water method and stained in various combinations of 

 colors. The most satisfactory preparations resulted from double 

 staining by means of the iron-haematoxylin method of Heiden- 

 hain, followed by eosin for a plasmatic stain. Gentian violet 

 and eosin also produced satisfactory images. Crushed, cover 

 glass preparations, stained like the sections, proved valuable 

 in the determination of details where the sections were not 

 satisfactory. 



Grateful acknowledgment is hereby made to Prof. W. M. 

 Wheeler for suggesting the line of investigation and for valu- 

 able assistance rendered in the prosecution of the same. The 



