546 



TEXT-BOOK OF ENTOMOLOGY 



These primitive regions of the primitive band, before the segments are formed, 

 are called by Graber macrosomites, and the secondary segments into which 

 they divide (which afterwards become the body-segments) , microsomites. The 

 macrosomites are peculiar to insects, and may be an inheritance from a hypo- 

 thetical ancestral form. With Korschelt and Heider, we should hardly share 

 this view. 



U N 

 NX 



Our observations on locusts show clearly (1) that the procephalic 

 lobes are 'the pleural portion of the first cephalic or antennal seg- 

 ment ; (2) that the antenna is an appendage or 

 outgrowth of the procephalic lobes; (3) that 

 the eyes are a specialized group of epidermal 

 cells of the upper part of the procephalic lobes, 

 and are not homologues of the antennae or of the 

 appendages in general ; and (4) it seems to fol- 

 low from a study of the relations and mode of 

 development of the clypeus and labrum, that 

 they arise between the procephalic lobes, and 

 probably represent the tergal part of the 

 antennal segment, forming the roof of the 

 mouth, i.e. closing in from above the pharynx. 



In general the formation of the body-segments 

 into the primitive band is in succession from 

 before to the hinder end. This successive 

 appearance has been observed by Graber in 

 genera of different orders (Stenobothrus, Lina, 

 and Hylotoma). For example, in the beetle 

 Lina, after the appearance of the mandibular 

 and two maxillary segments, appear the three 

 thoracic segments, together with the two ante- 

 rior abdominal segments, the other abdominal 

 segments arising afterwards. In other cases, 

 the formation of segments seems to be simul- 

 taneous along the entire length of the primi- 

 tive band. An exception to the rule has been 



bryo of (Ecanthus with the . . , TT T TT T , -, ,-, 



appendages budded out. noticed by Heider in Hydrophilus, as in tins 

 beetle the development of the segments of the 

 l U y> amnion c - middle region appears somewhat delayed, while 

 After Ayers. ^ j ore an( j j^nd parts of the primitive band 



are more rapid in development. In Pieris, according to Graber. 

 the thoracic segments are more rapidly developed than the others; 

 soon after, the gnathic segments (mandibles and two pairs of 

 maxillae) appear, and finally the abdominal segments are formed. 



FIG. 526. Older em- 



