EMBRYOLOGY OF COCCIDS 77 



Material and methods 



Three species of Coccidae belonging to three different genera 

 were chosen for the present investigation. These are: the 

 mealy bug, Pseudococcus mcdanieli Hollinger (ms.); Hunter's 

 Lecaniodiaspis, Lecaniodiaspis pruinosa (Hunter) ; the cottony- 

 cushion scale, Icerya purchasi Mask. 



The material of the mealy bug was obtained from its most 

 favorite host plant, the ragweed (Ambrosia trifida Linn.), on two 

 trips in the latter part of September and another in early October, 

 while that of Lecaniodiaspis was collected from time to time on 

 two elm trees on the campus of the University of Missouri, during 

 the season of 1917 to 1918. The cottony cushion scale was col- 

 lected from Acacia and Pitosporum found in the vicinity of San 

 Francisco Bay, California, during the seasons of January, 1915, 

 to May, 1917. 



Of the three species each had its own advantages. The eggs 

 of the mealy bug were very easUy fixed, sectioned, and stained, 

 but they were so small that it was difficult to dissect away the 

 chorions. The eggs of both the cottony cushion scale and Lecan- 

 iodiaspis are large, and the chorion can be removed easily. The 

 eggs of the Lecaniodiaspis, however, stain with considerable 

 difficulty. In fact, the egg of the cottony cushion scale was the 

 most favorable material, having none of the disadvantages above 

 mentioned. Yet it must be said here that it was with the study 

 of Lecaniodiaspis and to a considerable extent with that of the 

 Pseudococcus that the writer was able to see the true significance 

 of several organs and inclusions. 



The experunental method of determining the age of the embryo 

 was tried to a considerable extent with the cottony cushion scale. 

 For this purpose, about thirty adult females with the egg sacs 

 were collected, together with the infested twigs. After removing 

 the egg sac with a sharpened bamboo stick, the females were 

 placed in small paper boxes. Every five or ten minutes the 

 specimens were observed, and if an egg was seen protruding from 

 the vaginal orifice, it was transferred into a numbered gelatin 

 capsule. In the capsule, the egg was able to develop even to the 



