798 



THE 



Study of the development of the head sclerites. In 1866 he 

 argued that " since the arthropleural is the Hmb-bearing region 

 of the thorax it must follow that this region is largely developed 

 in the head," the sternites being reduced to a minimum and the 

 tergites almost completely absorbed. He believed that the bulk 

 of the head is formed " by the great expansions of the eye-pleu- 

 rites which, so to speak, are drawn back like a hood over the 

 basal rings." 



In 1870, in the second edition of his " Guide to the Study of 

 Insects (foot-note)," he reiterates these conclusions. He distin- 

 guishes the labrum, epipharynx, and clypeus as tergal elements 

 belonging to his hypothetical pre-ocellary segment. The occi- 

 put also is reckoned with the tergites, while the gula is sternal. 

 All of the other elements of the capsule are supposed to be 



Packard later completely revised his views as to the number 

 of primitive head segments. Instead of seven or a possible 

 eight, he recognized but four segments entering into the forma- 

 tion of this region. In 1883, in his paper on " The Number of 

 Segments in the Head of Winged Insects," he thus summarizes 

 his views as to the development of the sclerites : 



" It appears, then, that the epicranium or that piece (sclerite) 

 bearing the eyes, ocelli, and antennae, and in front of the clypeus 

 and labrum, is formed from the original procephalic lobes, and 

 represents the first or antennal segment ; while the remainder of 

 the original or primitive segments are obsolete, except in those 

 insects which retain traces of an occiput or fourth cephalic 

 tcrgitc. All of the gular region of the head probably represents 

 the base of the primitive second maxillae." 



Ayers ('83) refers to the reduction of the maxillary and man- 

 dibular segments, " their dorsal portions disappearing altogether 

 and their ventral portions fusing with the oral region." 



\'ia11anes ('86 and '87b) states that the head of an insect pre- 

 sents three prebuccal segments and that the labrum represents 

 the stetnite of the third or tritocerebral segment. Beyond this 

 he does not enter upon a discussion of the origin of the sclerites. 



Ikuler ('89) was the first to devote especial attention to the 

 development of the tentorium. His careful studies of the origin 



