32 SOME ASPECTS OF MORPHOLOGY 



the Insecta are features which seem to be correlated with 

 hexapodous locomotion. In the Symphyla (Fig. 18) the same 

 components of the leg are present as in the Insecta, but, on the 

 other hand, in the first-mentioned class the femora are very 

 short and the trochanters large and elongated. These same two 

 features are also betrayed in Lithobius, Scolopendra and other 

 Chilopoda, where they are correlated with polypodous locomotion 

 in these animals. Once an hexapodous condition is assumed it 



dc 



Fig. 18. Antepenultimate leg of Scutigerella. d, depressor of 

 trochanter ; dc, depressor of coxa ; I, levator of coxa ; st, stylus. 

 Other lettering as in Fig. 11. (From Ewing.) 



would appear that the trochanters lose some of their functional 

 importance, while the femora become larger and more powerful. 



D. The Cephalic Appendages, (a) The First Maxillae. The 

 generalised cephalic appendages are the first maxilla,^ and conse- 

 quently the morphology of these latter organs is of primary 

 significance in the interpretation of the homologies of the 

 remaining gnathal appendages. The first maxilla is divisible into 

 a basal region of complex structure bearing a serially segmented 

 distal organ or palpus. It is generally agreed that the palpus 

 represents the ramus or telopodite of a locomotory appendage. 



