FOLSOM : MOUTH-PARTS OF ANURIDA MAFxITIMA. 105 



The agreement between the finished mandibles of Campodea and 

 Japyx, on the one hand, and Coliemboh\, as represented by Anurida and 

 Orchesella, on the other hand, is remarkably close. In both groups the 

 mandible is hollow, has an oblique basal opening, which is large in Cam- 

 podea, and, instead of an ordinary articulation, a free basal pivot, which 

 is peculiar to the Apterygota. The homologies extend further, for I 

 find that the similar and complicated movements of the mandibles are 

 actually effected by muscles which are probably homologous in the two 

 groups. The equivalence of certain muscles in Campodea, as repre- 

 sented by Meinert ('65, Taf. XIV., Figure 15) with others figured by 

 myself for Orchesella (Folsom, '99, Plate 2, Figures 14, 15) may be ex- 

 pressed in tabular form as follows : — 



Campodea (Meinert). Orchesella (Folsom). 



Muscle C (distal) corresponds with 9. add. 

 " C (proximal) •' " l.rot.l. 



" D " " 5. pr't. I. and 6. pr't. ms. 



" E " " 3. ret. rot. and 4- I'^t., or else 7. rot. 



and 8. rot. 



The incompleteness of Meinert's figure prevents as exact a comparison 

 as is desirable. 



Japyx is nearest Campodea in structure, and the mandibles of Japyx, 

 which have been described and figured by Meinert ('65), Grassi ('86''), 

 and V. Stummer-Traunfels ('9l), are essentially like those of Campodea, 

 but lack the articulated lacinial lobe, there being a lacinial region, how- 

 ever, which (Grassi, "86^, Taf. II., Figura 14) is separated by a trans- 

 verse line from the fulcrum. The muscles of Japyx agree with those of 

 Campodea, and it is to be noted that the adductors originate upon a 

 median chitinous plate, or tentorium, just as in Collembola, but not as 

 in Orthoptera. The muscle/ of Meinert ('65, Taf. XIV., Figuren 5, 15) 

 has no homologue, it should be said, among the mandibular muscles of 

 Orchesella, and I should be disposed to regard it as an adductor of the 

 head of the first maxilla, had not v. Stummer-Traunfels ('91, Tiif. I., 

 Figuren 1, 3) figured the tendon of the same muscle in Campodea and 

 Japyx going to the mandible. This author ('91, p. 220) erroneously 

 states that the adductors of Collembola, Campodea, and Japyx are at- 

 tached to the " Stilt zapparate," by which he means the lingual stalks 

 (Plate 6, Figure 38, pd.^) ; these, however, are quite distinct from the 

 tentorium, which he apparently overlooked. 



Nearly allied to the entognathous genera Campodea and Japyx are 

 the ectoguathous genera Lepisma and Machilis. In Lepisma the early 



