EMBRYOLOGY OF COCCIDS 87 



4. CLEAVAGE 



The type of cleavage in the coccids studied is the pure super- 

 ficial type which is so common among the Arthropoda. The 

 first cleavage spindle lies at right angles to the shorter axis of 

 the egg, so that one of the two daughter cells arising from the 

 first division wanders toward the posterior pole while the other 

 cell remains near the position formerly occupied by the mother 

 nucleus (fig. 43). This behavior of the first two cleavage cells 

 in coccids is exactly like that of the termite studied by Knower 

 ('00). At first, all the cleaving cells were in the same mitotic 

 state, but gradually some lag behind others in division so that 

 in a later stage of cleavage, e.g., at the thirty-two cell stage, 

 more than one cleavage figure is noticeable among them (fig. 78) . 

 Up to about the eight-cell stage in the eggs of Lecaniodiaspis, 

 and to a still later stage in Pseudococcus and Icerya, these 

 cleavage cells are all at some distance from the cortical layers. 

 Although in each cell the nuclear membrane is distinct, the 

 cytoplasm presents numerous pseudopodial processes which con- 

 nect with those of neighboring cells. On account of their 

 somewhat isolated appearance, they are usually known as pro- 

 toplasmic islands. In eggs containing a large amount of yolk, 

 as, for example, those of Chrysomelid beetles studied by Hegner 

 ('14), the winter eggs of plant-lice investigated by Tarmreuther 

 ('07) and Webster and Phillips ('12), these protoplasmic islands 

 literally cut up the yolk into blocks. I have noticed this block- 

 like appearance of the egg contents in the living eggs of Lecanio- 

 diaspis, but upon sectioning them, I become convinced they 

 were not comparable to the yolk-blocks found, for example, in 

 the ova of aphids, because the eggs of Lecaniodiaspis contain no 

 yolk granules. The eggs of the mealy bug contain a darkly 

 staining substance resembling the yolk of the ova of aphids, but 

 they are never cut up into blocks b}^ the cleaving cells (fig. 42). 



Weismann ('82) stated that in Rhodites and Biorhiza aptera 

 (cynipids) , the first two cleavage nuclei move apart in the direction 

 of the longitudinal axis of the egg. One of them, upon reaching 

 the posterior pole of the egg, remain inactive and probably 

 degenerates, while the other, upon arriving at the anterior pole, 



