92 GEORGO ORIHAY SHINJI 



the body into four regions becomes plainly marked. A lateral 

 \dew of a somewhat older embryo is shown in figure 61 . Here the 

 abdominal region is so much elongated as to be actually folded 

 over beyond the thoracic part, and reaching almost to the base 

 of the second maxillae. The brain becomes very conspicuous, 

 owing to its enormous dorsal growth. Below the rudiment of 

 the brain another pair of elevations appears (fig. 65). This is 

 the rudiment of the first maxillae. Segmentation is clearly 

 visible throughout the oral, cephalic, thoracic, and the abdominal 

 regions. In a still older embryo (fig. 67) three pairs of appen- 

 dages become visible. These are the rudiments of the thoracic 

 legs. Thus the appendages of scale insects, like those of most 

 other insects, develop first from the maxillae backward to the 

 last thoracic limb and finally to the antennae and mandibles, 

 the labrum being the last to appear. In other words, the rudi- 

 ments of the second maxillae are the first to appear. The first 

 maxillae and the thoracic legs make an almost simultaneous 

 appearance, followed by the antennae, mandibles, and the 

 labrum. In this respect, the scale insects differ from the aphids, 

 in which, according to Mecznikow^ and Witlaczil, the antennal 

 appendages are the first to appear. The order of the appear- 

 ance of the appendages in Pseudococcus and other scale insects 

 differs also from that observed in the Orthoptera in which, as 

 described by ^Mieeler ('89), Riley ('98), and others, the antennae 

 are the first to appear, followed by oral appendages, the thoracic 

 limbs being the last to be formed. My observations also differ 

 from those made by Brandt on Libellulids, when the rudiment 

 of the thoracic limbs appears first, then those of the maxillae; 

 the antennae being the last to develop. In Coleoptera, i.e., 

 Hydrophilus, Melolontha, etc., according to Hej^mons and 

 others, the antennal rudiment seems to appear first, while the 

 mandibular and maxillary rudiments and those of the thoracic 

 legs make a simultaneous appearance. 



In Mantis (Hagen, '17) the antennal rudiments appear first, 

 followed by those of the thoracic appendages; then appear, 

 practically simultaneously, the rudiments of the maxillae and 

 labrmn, the last being distinctly an unpaired organ. 



