106 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY, 



development of the mandibles, as shown by Heymons ('97% Taf. XXX., 

 Figureu 13, 15, 17, 20), is simple, and agrees with that of Anurida and 

 Campodea. The finished mandible of Machilis (Oudemaus, '88, Plate 

 II., Figuren 25, 2G), especially, recalls that of Campodea and Collem- 

 bola by its elongated hollow fulcrum, oblique aperture, basal pivot, 

 distinct head, and (as in Orchesella) well-developed molar surface ; 

 moreover, the adductors originate on a tentorium and are inserted within 

 the mandibles (Oudemans, '88, Taf. 1, Figur 19; Wood-Mason, '79, 

 p. 148, Figure 1). Wood-Mason named the apex of the mandible " ex- 

 opodite " and the molar lobe " endopodite," but upon superficial grounds, 

 if one may judge from the evidence of embryology. Both lobes may 

 together represent the endopodite ; but the exopodite, or palpus, is un- 

 represented in the mandible, and it is a secondary lobe of the primary, 

 or stipal, fundament, in the first and second maxillaj. Wood-i\Iason 

 ('79) pointed out many interesting similarities which Machilis and 

 Lepisma bear to the most generalized Orthopteran family, the Blattidse, 

 and remarked (p. 149), concerning the pivot of Machilis, that "the pos- 

 terior ball-shaped condyle of mandibulated insects, clearly foreshadowed 

 in the myriapod, is here fully formed and provided with a distinct neck." 



The mandibles of Lepisma, however, more closely approach the Or- 

 thopteran type in being compact (v. Stummer-Traunfels, '91, Taf. II., 

 Figuren 5, G) and partly solidified, and in having broad incisive teeth, 

 a molar surface like that of Orthoptera, and broadly attached adductors. 

 The muscles are said by Oudemans ('88, p. 187) to resemble those of 

 Machilis. Y. Stummer-Traunfels represents the adductors only, and it 

 may well be that the muscles are really much fewer than in Campodea 

 and Collembola, such a reduction in number, if it occurs, being an 

 approach to the Orthopteran type, in which but two mandibular muscles 

 exist — a stout adductor and a slender abductor. 



As to the development of the mandibles in Orthoptera, very little has 

 been published. Ayers ('84, p. 241, Plate 18, Figures 20-22) says that 

 in OCcanthus "the three oral appendages arc trilobed ; the lobation is 

 most prominent in the second maxillary and least in the mandibular 

 appendage. The primitive appendage is first divided into two lobes, 

 and the inner of these becomes secondarily divided into two." The 

 three lobes doubtless represent palpus, galea, and lacinia. KorotnefT 

 ('85, Taf. XXIX., Figure 6) figures lobed mandiliular fundaments for 

 Gryllotalpa. In other Orthoptera such lobation has not been recorded. 

 In Platta, according to Wlicelcr ('89, p. 348), "There arc apparently 

 no traces of lobation in the mandibles." Packard ('83', p. 279) says, 



