28O FRANZ SCHRADER. 



not distantly related to Pseudococcus, suggested that they arise 

 from the yolk cells that is, cells that remain behind in the yolk 

 at the time of blastoderm formation. 



Strindberg ('19), who worked on Lecaniiim, reported that in 

 that coccid also, the mycetocytes took their origin in the yolk 

 cells. 



Pierantoni, who was the first worker to make a detailed investi- 

 gation of Pseudococcus gives a different account of the myceto- 

 cytes ('10, 'ii, and '13). According to him, some of the cleavage 

 cells in traveling to the periphery to establish the blastoderm, 

 encounter the symbionts. This association, more or less accident-^ 

 ally initiated, becomes permanent, and the cleavage cells assume 

 the characters that stamp them as mycetocytes. Exactly the 

 same process has been described by Pierantoni also in Icerya. 



Buchner ('21) in reviewing previous investigations, seems 

 inclined to agree with Pierantoni. 



Finally, Shinji ('19), also working on Pseudococcus, describes 

 a migration of cells to the symbionts, shortly before the germ 

 band commences its growth. These migrating cells he interprets 

 as potential germ cells. Some of them become permanently 

 associated with the symbionts and constitute the mycetocytes, 

 but others migrate once more to form the definitive gonads. 



In criticizing these varying results, I am not in a position to 

 pass judgment on the conclusions of Breest and Strindberg. 

 Certainly my own results in regard to the point in question, i.e., 

 the. origin of mycetocytes, have led me to an entirely different 

 interpretation. 1 But this difference may very well be due to an 

 actual difference in the development of mycetocytes in the three 

 genera under consideration. 



The work of the other investigators mentioned has already 

 been considered in a recent paper ('23). Although a considerable 

 part of that paper was devoted to showing that Shinji's conclu- 

 sions are untenable, I also took up briefly the statements of 

 Pierantoni. My own position on this question of the nature of 

 the mycetocytes can best be presented by giving a short resume 

 of those of my findings that are involved in the present discussion. 



In both Pseudococcus citri and P. maritimus, the somatic num- 



1 Regarding other points in the early development, I am in essential agreement 

 with Strindberg. 



