96 bulletin: museum of compakative zoology. 



Taf. II., Figureii 19, 29), and examples might be multiplied to show 

 that the labrum does not represent a pair of appendages. The view 

 held by Kowalevsky, Carriere and others, that it did, was based chiefly 

 upon anatomical evidence, which has since been disproved by Heymons 

 ('95) and others. (See Packard, '98, pp. 42-43.) 



Scolopendrella (Latzel, '84, p. 8, Taf. I., Figur 4; Grassi, '86*, p. 15, 

 Tav. II., Figura 6) has a simple, emarginate, six-toothed labrum, and, 

 like Hexapoda, a distinct, subtriangular clypeus. Moreover, as Packard 

 ('98, p. 22) has affirmed, it has a V-shaped tergal suture, which exists 

 also in the more generalized insects, but is absent in Myriopods. 



In "Diplopoda, an upper lip is present as a transverse plate, fused, 

 however, with the cranium. 



In Chilopoda, a similar labrum is pi-esent, but is not always basally 

 fused, and frequently consists of three transversely placed sclerites. It 

 originates as a simple median lobe (Heymons, '97^, p. 4, Figur l,Scolo- 

 pendra). 



In Crustacea the upper lip is derived from a median, unpaired evagi- 

 nation corresponding almost exactly in position with the labral funda- 

 ment among insects. 



Among insects, then, the labrum and clypeus develop from a median 

 evagination between the procephalic lobes, and give no satisfactory evi- 

 dence of paired origin. The same statement applies also to Crustacea, 

 and, as far as is known, to Myriopods. 



Antennae. 



The antennae are the first paired organs to appear. They develop 

 from the posterior boundaries of the procephalic lobes, and at Stage 1 

 (Plate 1, Figure 1, Plate 2, Figure 8, at.) are stout cylindrical papillje 

 already faintly constricted into two segments. As Figure 8 shows, they 

 are more lateral than the other paired fundaments, and at first far be- 

 hind the labrum. Sections prove them to be simple ectodermal evagina- 

 tions, like all the other appendicular fundaments. 



At Stages 2 and 3 (Plate 1, Figures 2, 3, at.) the anteimae are longer 

 and usually composed of three segments. In Figure 2 the fourth seg- 

 ment, which normally appears later than Stage 2, is suggested. They 

 have now moved forward to positions near the labrum ; in Stage 4 

 (Plate 1, Figure 4; Plate 3, Figure 12, at.) they lie on the two sides 

 of that appendage, and in Stage 5 (Plate 1, Figure 5 ; Plate 3, Figure 

 21, at.) they have attained a position farther forward than the upper lip. 



