=Number of segments in the head.=—While it is taken for granted by many entomologists that the head of insects represents a single segment, despite the circumstance that it bears four pairs of appendages, the more careful, philosophical observers have recognized the fact that it is composed of more than a single segment. Burmeister recognized only two segments in the head; Carus and Audouin recognized three; Macleay and Newman four; Straus-Durckheim even so many as seven. Huxley supposed that there are five segments bearing appendages, remarking, “if the eyes be taken to represent the appendages of another somite, the insect head will contain six somites.” (Manual of Anat. Invert. Animals, p. 398.) These discordant views were based on the examination of the head in adult insects; but if we confine ourselves to the imago alone, it is impossible to arrive at a solution of the problem. Newport took a step in the right direction when he wrote: “It is only by comparing the distinctly indicated parts of the head in the perfect insect with similar ones in the larva that we can hope to ascertain the exact number of segments of which it is composed.” He then states that in the head of _Hydroüs piceus_ are the remains of four segments, though still in the next paragraph, when speaking of the head as a whole, he considers it as the first segment, “while,” he adds, “the aggregation of segments of which it is composed we shall designate individually _subsegments_.” That the head of insects is composed of four segments was shown on embryological grounds by the writer (1871) and afterwards by Graber (1879). The antennæ and mouth-parts are outgrowths budding out from the four primitive segments of the head; the antennæ grow out from the under side of the procephalic lobes, and these should therefore receive the name of antennal lobes. In like manner the mandibles and first and second maxillæ arise respectively from the three succeeding segments. [Illustration: FIG. 34.—Embryo of _Anurida maritima_: _tc. ap_, minute temporary appendage of the tritocerebral segment, the premandibular appendage; _at_, antenna; _md_, mandible; _mx_^1, first maxilla; _mx_^2, second maxilla; _p_^1–_p_^3, thoracic; _ap_^1, _ap_^2, abdominal appendages; _an_, anus—After Wheeler. ] While the postoral segments and their appendages are readily seen to be four in number, the question arises as to whether the eyes represent the appendages of one or more preoral segments. In this case embryology thus far has not afforded clear, indubitable evidence. We are therefore obliged to rely on the number of neuromeres, or primitive ganglia. In the postoral region of the head, as also in the trunk, a pair of neuromeres correspond to each segment. (See also under Nervous System, and under Embryology.) We therefore turn to the primitive number of neuromeres constituting the procephalic lobes or brain.