EMBRYOLOGY OF COCCIDS 93 



The further growth of the appendages is shown in figure 47, 

 w^hich represents the surface view of a somewhat older embryo. 

 Mandibles, maxillae, and three pairs of thoracic legs are now 

 tubular instead of conical elevations. The second maxillae have 

 migrated somewhat dorsally and therefore are no longer in line 

 with the rest of the appendages, as was also noticed by Meczni- 

 kow ('66) for Lecanium. The three pairs of thoracic legs appear 

 somewhat constricted at the middle, indicating that they are, in 

 a sense, two segments. 



The first rudiment of the mouth is found in figure 49. This 

 is essentially a circular depression of the ventral plate in the 

 medial line between the rudiments of the brain elevations and is 

 cephalad of the oral or antennal appendages. 



Following this stage, the brain undergoes a conspicuous de- 

 velopment. Heretofore the rudiments of the brain were only 

 represented by two crescentic elevations, one on either side of 

 the median line. It now becomes a large conical structure, due 

 to its dorsal turning and rapid neurogenesis. It, however, lies 

 entirely within the serosa sac and not beyond the original 

 'blastopore' of Will, as he maintained was the case with the 

 development of the pseudo\aim of aphids. The brain region is 

 also surrounded, at least ventrally, by the amniotic layer. That 

 the rudiments of the antennae arise, not from the posterior end 

 of the brain, but from below it, is also clearly demonstrable 

 here. The segmentation of the abdominal region into its future 

 body segments is also clearly shown. 



In the next older embryo (fig. 95) several notable changes 

 are evident. The first maxillary rudiments have migrated still 

 further dorsally, lea\dng their alignment with the rest of the 

 appendages. The three pairs of thoracic limbs now present a 

 slight constriction approximately at the middle of the appen- 

 dages. The segmented abdominal region is still folded over the 

 thoracic as well as the oral regions. 



Following this stage, the embryo gradually shortens until it 

 begins to rotate around ihe transverse axis of the egg. As a 

 result of this rotation, the poles of the egg coincide with those 

 of the embryo (figs. 53, 72). Heretofore, the cephalic or anterior 



