folsom: mouth-pakts of anurida maritima. 97 



In Stage 6 (Plate 1, Figure 6, at.) there is clearly indicated a fourth 

 antennal segmeut, which in Stage 7 (Plate 2, Figure 7 ; Plate 4, Figure 

 24, at.) becomes more distinct. At this time the antennae are long and 

 stout, and occujjy a position still farther forward than before. 



At hatching (Plate 6, Figure 41) they are pre-oral, more slender, dis- 

 tinctly segmented, and clothed with setae. 



Elongation of the antennae occurs throughout their entire length, 

 judging from the number of cells in longitudinal alignment on the same 

 segment at difterent stages of growth, and also from the frequency of 

 karyokinesis in different parts of the appendage. Growth is more rapid, 

 however, in the apical region, from which the segments are successively 

 constricted. In all the oral fundaments, in fact, growth was inferred to 

 be most rapid at the apex, although likewise occurring throughout the 

 rest of the ectodermal layer. At the apex itself — and these remarks 

 apply equally well to the legs — the hypodermal cells are larger and 

 more turgid than elsewhere, projecting as minute lobes from the surface. 

 The chromosomes are very small, but frequently so arranged as strongly 

 to suggest mitotic division. 



At Stage 5 (Plate 4, Figure 28, deu'ceh.) an antennary ganglion sup- 

 plying the antennal nerves, becomes evident, but finally fuses with the 

 first and third ganglia, between which it lies, to form the supraoesophageal 

 ganglionic mass. 



In Thysanura the antennae develop essentially as I have described for 

 Collembola, being likewise at first post-oral and subsequently pre-oral, as 

 Uzel ('98) has shown for Campodea and Heymons ('S?"*) for Lepisma. 

 Such a migration of the antennae is, however, not peculiar to Aptery- 

 gota, but is characteristic of all insects. 



Among Diplopoda but a single pair of antennal fundaments occurs 

 (Heymons, '97^, p. 7, Figur 2, Glomeris). Judging from their position 

 in relation to the mouth, they are equivalent to the antennae of Chilo- 

 poda, among which Heymons ('97'', p. 4, Figur 1, Scolopendra) has 

 discovered two pairs of antennal fundaments. The prae-antennal rudi- 

 ments in Chilopoda appear to represent the antenn£e of insects and the 

 antennules of Crustacea, the second pair to be equivalent to the inter- 

 calary appendages of insects and the antennae of Diplopods and of 

 Crustacea. 



It can scarcely be doubted, in view of the researches of Viallanes ('87), 

 that the antennae of insects are homologous with the antennules of Crus- 

 tacea. In the author's words ('87, p. 105): " Voyons maintenant le 

 deuxieme renflemeut cerebral du Crustace decapode. II est forme d'une 



