INSECTA. 



895 



the form and relative size of parts of the head oc- 

 curs in the hog-beetles, Curculionida (Jig. 337), 

 in which the head is elongated forwards, and 

 the mouth is situated at the extremity of a long 

 rostrum or beak. This is occasioned by the 

 narrowing and extension forwards of the clypei, 

 and the parts corresponding to them, the men- 



turn and sub-mentum. This change is carried 

 to such an extent in some species, as in Liparis 

 Germanus, that the antennae are also carried for- 

 wards, and appear as if situated at the sides of 

 the mouth. That this is the manner in which 

 the change of form is effected is proved by the 

 circumstance, that the basilar and epicranial 

 regions in this insect do not exceed a fair pro- 

 portion, as compared with other insects; while 

 the triangular suture, which always divides the 

 epicranium from the posterior clypeus, exists in 

 its usual situation on the part between the 

 eyes ; and the labrum, which is very distinct, is 

 freely articulated with the anterior margin of 

 the clypeus. The effect of this elongation of 

 some parts of the head and mouth is the neces- 

 sarily small size of others, and consequently we 

 find that the mandibles, which are so enor- 

 mously large in Lucanus, are reduced almost to 

 their minimum in the Curculio ; because, al- 

 though the elongated form of the head is admi- 

 rably adapted to the habits of the insect, in 

 boring deeply into hard substances, it is insuffi- 

 cient for the support of large and powerful 

 organs, and its extent of surface is too limited 

 to afford adequate room for the muscles neces- 

 sary for their employment. Wherever large 

 and powerful organs exist, the parts to which 

 they are attached are enlarged in like manner. 

 Thus we invariably find that in those insects in 

 which the mandibles are large, the whole head 

 is either short and wide, or its posterior por- 

 tions, the basilar and epicranial regions, to 

 which the muscles of the mandibles are at- 

 tached, greatly exceed those of the anterior. 



The parts observed in the head in Coleop- 

 tera are equally apparent in Onhoptera. In 

 this order the head is placed vertically on the 

 pro-thorax, without any constricted portion or 

 neck, so that the extent of the occipital region 

 is greatly reduced. The epicranium in some 

 species, Locustid<e, $c. is broad behind, but 

 narrowed in front, where it is bounded, as in 

 other insects, by the clypeus posterior, and la- 

 terally by the cornea? and sides of the head, of 

 which it forms a part. In this order the 

 ocelli, or single cornea?, which are found only 

 in a few solitary instances in Coleoptera, exist 

 in most of the families. They are situated in 

 the anterior portion of the epicranium, and 

 form part of its surface, whether placed on the 

 vertical portion of the head, or more anteriorly 

 near the clypeus. In the osculant family, 

 Blattida, the epicrauium is exceedingly 

 shortened, but retains along its vertex a trace of 

 the epicranial suture, which is scarcely ever 

 absent in the insects of this order. It is very 

 distinct in the common house-cricket and mole- 

 cricket, Achetida; (Jig. 342), in the Gryllida: 

 and Locustida. In the mole-cricket it some- 

 times appears as if wholly obliterated, but is 

 always seeu in the pupa if care be taken to 



remove the down with which it is sometimes 

 covered. Its apex is situated in the middle 

 line between the ocelli, and on each side it 

 passes down to the insertion of the antennae. It 

 is in this order that the suture is particularly 

 useful in indicating the boundary of the pos- 

 terior clypeus, the extent of which in Orthop- 

 tera appears hitherto to have been overlooked. 



Fig. 373. 



Head of Blatta Americana. 



A, antenna ; t, tympanum ; 1 1 socket for the an- 

 tenna, covered with membrane ; dd, clypeus, 

 anterior and posterior; *, lingua; **, paraglossae. 

 ( Other letters and figure* at in Hydrous. ) 



In the epicranium of Blatta (Jig. 373), the 

 suture is almost obliterated, being only disco- 

 verable by aid of the microscope, but on careful 

 inspection it is seen to end at a point opposite 

 to the middle of the superior portion of the 

 corneae, where it forms the apex of the triangle, 

 which enters, on each side, the anterior margin 

 of a circular space covered with a tense mem- 

 brane, the tympanum (f), which is situated, as 

 observed by Treviranus, a little behind the in- 

 sertion of the antennse. These organs are also 

 inserted in a rounded space covered by a mem- 

 brane. From these points the suture becomes 

 obliterated, but seems to pass in the direction 

 of the anterior boundary of the corneae to the 

 base of the mandibles. The clypeus posterior 

 (d) thus appears to form the greater portion of 

 the front or face of the insect, and is united by 

 a transverse freely articulating membrane, ex- 

 tending across from the base of each mandible 

 with a short transverse plate, the clypeus ante- 

 rior (d), which has hitherto been looked upon 

 as the true clypeus. In the common green 

 grasshopper, Acrida viridissima, the boundary 

 of the posterior clypeus is at the most anterior 

 part of the head immediately between the an- 

 tennae, the suture extending, as in other in- 

 sects, to their base. The clypeus anterior is a 

 short transverse moveable plate, and is articu- 

 lated with the labrum (e\ which is also short, 

 transverse, and freely moveable upon the cly- 

 peus anterior. This moveable condition of the 

 anterior clypeus and lip has not a little puzzled 

 entomologists. Mr. Newman* has remarked 

 that " the lip and shield move simultaneously 



Op. cit. p. 9. 



