NO. 3 



INSECT HEAD SNODGRASS 



87 



and a subcoxa (fig. 34 B, Cx, Sex), and Borner (1909, 1921) would 

 identify the cardo of the maxilla with the subcoxa of a leg. The suture 

 separating the cardo from the stipes, however, terminates at both 

 ends in the marginal rim of the maxillary base (fig. 35 A) instead 

 of running parallel with it; the cardo, therefore, does not have the 

 relation of a true segment to the rest of the appendage. It is perhaps, 



Fig. 35. — The relation of a maxilla to a generalized limb. 



A, theoretical generalized structure of a gnathal appendage, consisting of a 

 limb base (LB), bearing a divided basendite (Lc, Ga), and a six-segmented 

 telopodite, or palpus (Pip), with the principal downward flexure at the femoro- 

 tibial joint (ft). The limb base provided with tergal promotor and remotor 

 muscles (/, /), and sternal adductors (KL). 



B, showing basal musculature of a gnathal appendage analysed into the 

 functional elements of the musculature of an annelid parapodium (fig. 33 D). 



C, third maxilliped of Apus longicaxidata, left, anterior surface, showing 

 division into a limb base (LB) and a telopodite (Tip) ; the base movable on a 

 transverse axis (a-b), the telopodite with a principal flexure (ft) between its 

 third and fourth segments. 



a-b, basal axis of limb base; Be, basendite; ct, coxo-trochanteral joint; F, 

 femur ; fga, flexor of galea ; flee, cranial flexor of lacinia ; flcs, stipital flexor of 

 lacinia; ft, femoro-tibial joint; Ga, galea; /, tergal promotor; /, tergal 

 remotor; K, sternal promotor; KL, ventral adductors (K and L united); L, 

 sternal remotor ; LB, limb basis ; Le, lacinia ; O, levator of telopodite ; Pip, 

 palpus (telopodite) ; Q, depressor of telopodite; Tip, telopodite; Tr, trochanters. 



though, to be questioned if the subcoxa! chitinization, the pleuron, at 

 the base of a thoracic leg is not also a mere subdivision of the basal 

 limb segment similar to the cardo, rather than the remains of a true 

 independent segment. If the cardo does, in any sense, represent the 

 thoracic subcoxa, it is to be noted that the hinge line between it and 

 the stipes has a horizontal position with reference to the axis of the 

 appendage, and this, the writer has argued (1927), must have been 

 the primitive position of the subcoxo-coxal hinge in a thoracic leg. 



