404 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



the lateral ones run to the lateral wall of the head, and the most distal 

 of the three median ones runs to the branch of the fulcrum support- 

 ing the clypeus, whereas the other two median ones meet the cor- 

 responding ones from the opposite side beneath the oesophagus. They 

 may correspond to the muscles h in the two preceding groups. 

 An endosternum has not been seen by me, but may be present. 



From this it will be seen that the mandibles of the Diplura and 

 Collembola are rather closely alike both in themselves and as regards 

 their muscles, whereas the mandibles of Protura have a different mus- 

 culature, are not hollow, and have no teeth. The mandibles of Pro- 

 tura are piercing organs necessitating especially strong protracting and 

 retracting movements ; and this, in connection with the probably sec- 

 ondary fact that they are not hollow, may account for the difference. 



5. THE MAXILLAE 



In Diplura the maxillae are hollow at their inner and upper sides. 

 The basal rod is commonly called cardo ; I have already mentioned 

 that it is placed dorsally to the lateral proximal arm of the fulcrum. 

 Since Meinert (1865), nearly all authors have regarded it as a cardo, 

 the only exception known to me being Silvestri ( 1933) ; in figure IVi_3 

 (P- 336) he designates a small proximal triangle of the stipes as 

 cardo and does not give any name to the rod commonly called cardo. 

 This small triangle is also seen by Hansen (1930, p. 129 and pi. VI, 

 fig. lb, cp), who calls it a "chitinized piece" and considers it a firmly 

 chitinized small part of the membranous lateral wall of the head. It 

 is not present in Campodea nor does it seem to me to be present in 

 Japyx; at least in the cases I have seen myself — among which is 

 also the slide made by Hansen and used for his figure — this piece is 

 intimately connected with the cardo by weaker chitin. 



A strong rod like a V with unequal arms forms the proximal end of 

 the maxilla (figs. 5 and 6). The longer arm goes to the lacinia, the 

 shorter arm continues in a weak part, the basal part of the palpus 

 and galea, which are both well developed ; in Japyx the palpus is even 

 segmented. The palpus and galea are covered with hairs and are free 

 of the mouth cavity. 



This is the common explanation of the maxilla, and it seems to me 

 quite natural; still Denis (1949) regards the whole piece between the 

 fulcrum and the outer side of the palpus as the maxilla (called cx^, 

 premier coxa, by him), in which case the so-called cardo would be 



