MORPHOLOGY OF THE MANDIBLES 



61 



A 



He also refers to the prostheca of Kirby and Spence (Fig. 49), 

 which he thinks appears to be a mandibular lacinia homologous with 

 it in Staphylinidae and other beetles (J. B. Smith also considers it 

 as "homologous to the lacinia of the maxilla"), and on examining 

 it in P. cornutus and a Nicaragua species (Fig. 49), we adopt his view, 

 since we have found that it is freely movable and attached by a 

 tendon and muscle to the galea. In the rove beetles (Goerius, Staphy- 

 linus, etc.) and in the subaquatic Heteroceridae, instead of a molar 

 process, is a membranous setose appendage not unlike the coxal 

 appendages of Scolopendrella, movably articulated to the jaw, which 

 he thinks answers to the molar branch of the jaws in Blatta and 

 Machilis. " It has its homologue in the diminutive Trichoptery- 

 gidye in the firmly chitinized quadrant-shaped sec- 

 ond mandibular joint, which is used in a peculiar 

 manner in crushing the food " ; also in the movable 

 tooth of the Passalidse, and 

 in the membranous inner 

 lobe of the mandibles of 

 the goliath-beetles, etc. 



J. B. Smith has clearly 

 shown that the mandibles 

 are compound in certain of 

 the lamellicorns. In Copris 

 Carolina (Fig. 50), he says, 

 the small membranous 

 mandibles are divided into 

 a basal piece (basalis), the 

 homologue of the stipes in the maxilla; another of the basal pieces 

 he calls the molar, and this is the equivalent of the subgalea, while 

 a third sclerite, only observed in Copris, is the conjunctivus, the 

 lacinia (prostheca) being well developed. Smith therefore con- 

 cludes "that the structure of the mandible is fundamentally the 

 same as that of the labium and maxilla, and that we have an equally 

 complex organ in point of origin. Its usual function, however, 

 demands a powerful and solid structure, and the sclerites are in 

 most instances as thoroughly chitinized and so closely united to 

 the others that practically there is only a single piece, in which the 

 hornology is obscured." (Trans. Amer. Ent. Soc., xix, pp. 84, 85. 

 1892.) From the studies of Smith and our observations on Staphy- 

 linus, Passalus, Phanaeus, etc. (Fig. 50, A, B) we fully agree with 

 the view that the mandibles are primarily 3-lobed appendages like 

 the maxillae. Nymphal Ephemerids have a lacinia-like process. 

 (Heymons.) 



Fio. 49. Mandible of Pax/talus cornntus with the 

 prostheca (!) : A, that of a Niearaguan species ; a, inside, 

 \>, outside view, with the muscle. 



