INSECTA. 



909 



the clypeus posteriorly, which is reduced to a 

 small triangular plate (d) with its apex directed 

 backwards. It is divided by a transverse suture 

 from the clypeus anterior, which forms a chief 

 part of the front of the head. The labrum (e\ 

 as in the preceding species, is short and pointed, 

 the mandibles (J'} are long and setiform, but 

 Jarger than the maxillae (g), and the lingua (*), 

 according to Savigny's observations, forms a 

 short trifid process within the cavity of the 

 mouth, at the base of the maxillae, the covering 

 or sheath to the parts being formed, as in the 

 other species, by the labium. 



In Homoptera, which are considered by 

 many naturalists as constituting only a division 

 of the Hemiptera, the general form of the head 

 is that of a triangle, the lateral and basilar 

 angles of which are occupied by the protu- 

 berant corneas. In the Cicadiida the epicra- 

 nium is short but exceedingly wide, bearing at 

 its sides on distinct pedicles the large project- 

 ing corneae similar to the pedunculated eyes of 

 Diopsis, one of the Diptera. The epicranial 

 suture is most distinctly marked. It passes 

 outwards from the middle line on each side 

 behind a large, convex, transversely striated 

 protuberance on the front, which is the proper 

 clypeus posterior, as far as the base of the 

 pedunculated corneae, where the antennae are 

 inserted immediately in front of it. The ocelli, 

 three in number, arranged in a triangle, are 

 placed on the most vertical part of the epicra- 

 nium, and the suture passes through the ante- 

 rior one. The clypeus anterior is a short 

 triangular plate, united by suture to the anterior 

 margin of the clypeus posterior. It has usually 

 been described as the labrum. The proper 

 labrum is a small pointed corneous plate, which 

 covers the base of the proboscis in front, and 

 is freely articulated to the margin of the clypeus. 

 It has been figured by Messrs. Kirby and 

 Spence* as an appendage to the labrum (appen- 

 dicula), which, as just shown, is the clypeus 

 anterior. It is often partially concealed beneath 

 the clypeus. The mandibles and maxillae are 

 usually strong corneous setae, contained within 

 the sheath formed by the labium. At the base 

 of the maxillae, concealed by the labium, are 

 two short membranaceous appendages, which are 

 probably the rudimentary maxillary palpi. They 

 are attached to the external under surface of 

 the maxillae, and are entirely concealed by 

 the labium. In the Fulgorida, as in Fulgora 

 candelaria, the epicranial region constitutes the 

 greater portion of the head. The large curved 

 process or horn on the front is derived entirely 

 from the epicranium. The cornea, which are 

 remarkably protuberant, are included within 

 the same region at the sides of the head, as 

 also are the two ocelli, which are placed one 

 on each side immediately before the corneae. 

 The antenna present a remarkable character, 

 being formed of three short thick joints, ter- 

 minated by a minute setaceous one. The third 

 joint, which is nearly globular, is covered with 

 minute protuberances, somewhat resembling 

 the structure of the corneae, or rather that of 



* Introduct. vol. iii. pi. 6, fig. 7, a. 



the antennae in the males of Eucera longicornis. 

 These organs are situated in deep fossae, into 

 which the triangular suture enters. The clypeus 

 posterior forms the chief portion of the front, 

 as in the preceding family, the clypeus anterior 

 a narrow plate united to the latter by suture, 

 and the labrum a small triangular appendage. 



We have entered thus minutely into an 

 examination of the parts of the head and mouth 

 in the different orders of insects, in consequence 

 of the uncertainty which has hitherto existed 

 among naturalists with regard to the number of 

 segments of which the head is normally com- 

 posed, and also because it was necessary that 

 we should first show the analogous parts of the 

 head in the different orders before stating our 

 opinions with regard to the manner in which 

 they are developed ; and further, because from 

 the minuteness of the subjects and consequent 

 difficulty of investigation, the most ample 

 elucidation was necessary upon which to base 

 our opinions. 



In our examination of the remaining parts 

 of the skeleton the same minuteness will be of 

 less consequence, because the parts are more 

 easily examined, and have already been identi- 

 fied through the excellent and elaborate investi- 

 gations of Audouin, Macleay, and others. 



Developement of the head. We have seen 

 in our examination of the perfect insect, that the 

 head is normally composed of four, and appa- 

 rently even of five sub-segments, as is proved 

 by the existence of the parts we have de- 

 scribed, which correspond to the superior and 

 inferior arches of that number. The first, or 

 most anterior of these sub-segments, is formed 

 by the labrum above and the ligula below the 

 second, by the clypeus anterior and the men- 

 turn ; the third, by the clypeus posterior and 

 submentum. But the fourth, which has be- 

 come entirely atrophied, is represented above 

 only by the little bones of the antennae, within 

 the cranium, and perhaps also the corneae; and 

 below by that reduplicature of tegument which 

 forms in some insects, as in Hydrous, the large 

 transverse bone, or ridge between the submen- 

 tum and anterior margin of the gula; while the 

 fifth is formed by the epicranial region above, 

 and the gula and broad basilar region below, 

 the greater size of this sub-segment being the 

 result of its confluence with the preceding one, 

 the fourth, which has disappeared. The num- 

 ber and position of these parts are precisely 

 similar in the larva and the perfect insect, as 

 seen in Coleoptera, Hymenoptera, and the ver- 

 miform larvae of Diptera. In each of these 

 instances the greater or less distinctness of the 

 parts is in an inverse ratio to the more or less 

 perfect organization of the individual. Thus, 

 if we take, for example, the head of the larva of 

 the common Chaffer-beetle, Melolontha, the 

 first, second, third, and fifth sub-segments are 

 very distinct, and the antennae, inserted at the 

 angles of a strongly marked triangular suture, 

 indicate the situation of the fourth atrophied 

 sub-segment. But in the perfect beetle, as we 

 have formerly seen, not only have all these se- 

 parate parts of the larva become confluent, but 

 their previous existence as distinct pieces is 



