STUDIES ON INSECT SPERMATOGENESIS. 73 



across, appearing with diagrammatic clearness (Fig. 20). In 

 early stages I have counted at least 15 to 20 such thread sections 

 in a single half of the nebenkern. At this same stage Kopsch 

 preparations are sometimes obtained in which the chromophobic 

 substance is very intensely blackened while the threads are left 

 clear. Thus a picture exactly the reverse of the Cajal result is 

 obtained. (Compare Figs. 17 and 20 with Figs. 18 and 19.) 

 With the elongation of the nebenkern the threads spin out along 

 its course and show a progressive decrease in number, as can be 

 clearly demonstrated in cross-sections (compare Figs. 20 and 24), 

 as well as in plane views (Fig. 23) of the nebenkern. They now 

 show the beaded appearance perhaps due to their origin from 

 chains of separate vacuoles, in a very characteristic manner. It 

 is not easy to say at this stage just how the reduction in the num- 

 ber of threads takes place, but there appears to be a side by side 

 fusion of adjacent threads, a single thread thus arising from two 

 preceding ones. This fusion goes on rapidly until at the stage 

 when the tail vesicles (see beyond) are first formed, the threads 

 of each half of the nebenkern have fused to form a single axial 

 core for their respective nebenkern portions (Figs. 25 and 26). 

 In the final condensation o>f the threads proof of the lateral fusion 

 of the separate threads can be obtained ; for in stages just prior 

 to that of Fig. 26 the threads will, in some places along their 

 course, be already fused to form a single axial core, while in 

 other places they are still clearly separate. Paulmier ('99) noted 

 this central core in the elongating nebenkern halves of Anasa, 

 likening it to " a long vacuole extending down each one." 



The origin of these threads (central substance) seems to have 

 been studied only by Holmgren, and Vejdovsky. In Silpha, ac- 

 cording to Holmgren ('02) there is, in each half of the nebenkern, 

 a single, beaded thread, which arises from the central chromo- 

 philic mass by a process of splitting off. To these thread-like 

 portions thus separated off is given the name of " Mitochondrien- 

 balken." Slightly later the chromophilic mass disappears as I 

 have already noted above, and the threads now occupy the halves 

 of the divided nebenkern exactly as I have described the arrange- 

 ment in Hemiptera. Holmgren figures also a number of cross- 



