No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. II 



The serosal fold continues to advance from all sides till the 

 organ is entirely covered. Viewed from its ventral surface 

 the egg now has the appearance of Fig. 4 (Stage D). Here 

 the indusium is cordate in outline and somewhat larger than 

 usual. Of the abdomen only the two basal segments still 

 remain on the ventral face of the egg ; the remaining seg- 

 ments curl back into the yolk. 



During this and the two preceding stages the cephalic and 

 thoracic appendages have become distinctly established as 

 rounded lateral outgrowth of their respective segments. The 

 antenna {at) originate as lobular outgrowth from the posterior 

 edges of the procephalic lobes. They are distinctly postoral 

 in origin. The margins of the triangular oral orifice are some- 

 what swollen; the anterior edge, where the labrum is about 

 to appear, is cleft in the median line (Fig. 16). The three 

 thoracic segments are very slightly or no broader than the two 

 maxillary segments. The appendages of these five segments 

 are also alike in size, shape, and position. In very early stages 

 of other insect embryos, even before the amnion and serosa 

 are fully formed, the thoracic become broader than the maxil- 

 lary segments, and the legs, as soon as they appear, may be 

 readily distinguished from the two pairs of maxillae by their 

 greater size and prominence. The Locustid embryo, there- 

 fore, has even a stronger tendency to revert to annelid-like or 

 myriopod-like ancestors than is apparent in any of the other 

 insects whose ontogenies have been investigated. 



The mandibular segment of XipJiidium like that of other 

 insects, is somewhat retarded in its development. Between 

 this and the antennary segment careful study of sections and 

 surface preparations reveals the presence of another segment, 

 shown very distinctly in outline in Fig. 16 (/r. J-.). This is 

 no other than what I have called the intercalary segment in 

 Doryphora. It is the tritocerebrum of Viallanes ('90^- '90^). 



The embryo continues to move back into the yolk, fol- 

 lowing the curved path established by the inflexion of the 

 posterior segments till its tail is finally arrested by striking the 

 serosa on the dorsal surface. At this time the embryo has the 

 form of an arc subtending the dorsoventral diameter of the ^%g. 



