126 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



formulated a significant law — " dass man drei Glieder ini Stamm von 

 alien gespalteteu Gliedmassen bei den Crustaceen als eiu primares 

 Verhaltniss annehmen muss, nnd diese Zahl hat sich, wenigstens in 

 den angefiihrten Fallen, deutlich erhalten." In fact, Hansen himself 

 (p. 206) has homologized the first maxillce of Machilis with the second 

 maxilke of Crustacea, on account of the three axial segments and the 

 position of the palpus, saying : " Der Bau der Maxillen . . . stimrat 

 also genau mit den Maxillen der Eumalacostraken." 



The axial segments of the Crustacean appendage are on this view- 

 successively equivalent to cardo, stipes, and palpifer of Hexapoda. 



It must be admitted that these anatomical agreements, if appealed to 

 alone, may logically be used to support other views than my own, since 

 all the Crustacean appendages are constructed upon the same plan ; but 

 the equivalence of the neuromeres in Hexapoda and Crustacea is a mat- 

 ter of the greatest significance. Viallanes has proved that the first three 

 neuromeres in the two groups agree in great detail, and I find that his con- 

 clusions apply equally well to the succeeding neuromeres. It is very sig- 

 nificant that in most cases the appendages of equivalent somites have 

 the same function in the two groups, and that all the paired nerves of 

 the head in Collembola agree exactly in position with those of decapod 

 Crustacea. 



Summarizing : The first maxillae of Apterygota develop in all essential 

 respects like those of Orthoptera, with which they may be homologized 

 in detail. In Anurida a palpus appears, but is resorbed before hatching, 

 indicating the descent of Anurida from a form in which the first maxil- 

 lary palpi were functional. The first maxillce of Campodea are clearly 

 to be homologized with those of Scolopendrella, and less clearly with 

 the lateral portions of the Diplopod guathochilarium. The first maxilhe 

 of Hexapoda pass through a biramous stage, such as obtains among 

 Crustacea, are comparable with Crustacean second maxillre in some 

 detail, and are homologous with those of Malacostraca. 



Labium. 



The fundaments of the labivnu, or "second maxillae," appear next 

 after tliose of the first maxillre, and at Stage 1 (Plate 1, Figure 1 ; 

 Plate 2, Figure 8, mx.^) are a pair of simple conical elevations rising 

 perpendicularly from the germ band and slightly longer than the funda- 

 ments of the mandibles and first maxillae. In the following stage (2) 

 they are longer and more cylindrical (Figure 2) ; in Stage 3 (Figure 3) 



