108 GEORGO ORIHAY SHINJI 



In the case of Icerya, the symbiotic organisms appear in a 

 somewhat different manner, especially as regards the place where 

 they first enter. A brief account of the mode and place of 

 entrance of the Iceryian form, therefore, may not be out of place. 



In the cotton}'- cushion scale, the symbiotic organisms first 

 appear, not around the anterior, but at the posterior end of the 

 egg. The method of entrance is, however, essentially the same 

 as in the case of Pseudococcus and Lecaniodiaspis already men- 

 tioned. After their liberation from the cytes, the rod-like 

 organisms migrate through the epithelial layer surrounding the 

 posterior end of the egg. In figure 35 several stages in the migra- 

 tion of these rod-like organisms into the egg are shown. These, 

 like those of Pseudococcus, stain exceedingly darkly with iron 

 alum haematoxylin or any other nuclear stain, and consequently 

 their finer structure is difficult to make out. Nevertheless, more 

 favorable specimens show at least three regions in each of them. 

 These are the outer somewhat lightly staining portion, probably 

 representing cytoplasm; the inner more densely staining region, 

 resembling the nuclear region ; and a central denser region, proba- 

 bly representing chromatic matter. Since, as stated, the symbi- 

 otic organisms, in the case of the cottony cushion scale, become 

 localized near the posterior end of the egg, where the invagination 

 of the germ band occurs soon after the final settlement of the 

 organisms, the germ cells come into contact with the parasites 

 without migrating far. But, since now the germ cells and the 

 symbiotic organisms are situated at the point of invagination, 

 they both become actually pushed into the egg further and fur- 

 ther, as the invaginating germ band elongates (figs. 62 to 67), 

 until they become similarly located as in the mealy bug and 

 Lecaniodiaspis. As soon as they reach this point, a short distance 

 from the anterior pole of the egg, they become stationary and do 

 not accompany a further extension of the caudal portion of the 

 embryo. This fixed point corresponds, as in the case of other 

 scale insects, with the third and fourth abdominal segments of 

 the embryo, larva, and adult. The history of these organisms 

 from this time on is an exact repetition of what has been 

 described for the other two species. 



