From the researches of Patten, Viallanes, and of Wheeler, especially of Viallanes, it appears that the brain or supraœsophageal ganglion is divided into three primitive segments. (See Nervous System, Brain.) The antennæ are innervated from the middle division or deutocerebrum. Hence the ocular segment, _i.e._ that bearing the compound and simple eyes, is supposed to represent the first segment of the head. This, however, does not involve the conclusion that the eyes are the homologues of the limbs, however it may be in the Crustacea. The second head-segment is the antennal, the antennæ being the first pair of true jointed appendages. The third segment of the head is very obscurely indicated, and the facts in proof of its existence are scanty and need farther elucidation. Viallanes’ tritocerebral lobes or division of the brain is situated in a segment found by Wheeler to be intercalated between the antennal and mandibular segments. He also detected in _Anurida maritima_, the rudiments of a pair of appendages, smaller than those next to it, and which soon disappear (Fig. 34, _tc. ap_). He calls this segment the intercalary.[12] Heymons (1895) designates it as the “Vorkiefersegment,” and it may thus be termed the premandibular segment. [Illustration: FIG. 35.—Head of embryo of honey bee: _B_, a little later stage than _A_. _pr.m_, premandibular segment; _cl_, clypeus; _ant_, antenna; _md_, mandible; _mx_, first maxilla; _mx′_, second maxilla; _sp_, spiracle.—After Bütschli. ] As early as 1870 Bütschli observed in the embryo of the honey bee the rudiments of what appeared to be a pair of appendages between the antennæ and mandibles, but, judging by his figures, nearer to and more like the mandibles than the rudimentary antennæ (Fig. 35); they seemed to him “almost like a pair of inner antennæ.” “I find,” he says, “in no other insects any indication of this peculiar appendage, which at the time of its greatest development attains a larger size than the antennæ, and which, afterwards becoming less distinct, forms by fusion with that on the other side a sort of larval lower lip. That this appendage does not belong to the category of segmental appendages is indicated by the site of its origin on the upper side of the primitive band.” (Zeitschr. wissen. Zool., xx, p. 538.) Grassi has also observed it in Apis, and regards it as the germ of a first, but deciduous, pair of jaws. In the embryo of Hylotoma Graber (Figs. 134, 135) found what he calls three pairs of “preantennal projections,” one of which he thinks corresponds to the “inner antennæ” of Bütschli. This subject needs further investigation.