FIG. 1. Machilis polypoda, from Sir J. Lubbock, Monograph of the Collembola and Thysa-nura, Ray Society, 1873, Pl. LIII. and p. 236.
Plate IX. Arthropoda.
This Insect belongs to the order Thysanura, family Lepismidae. The many jointed filaments borne by the last abdominal somite in this order are three in number, except in the genus Campodea, where they are two, and in Iapyx, in which they are represented by a pair of short stout un-jointed forceps. In Lepisma the three filaments are equal in size; in Lepismina and Nicoletia the central filament is slightly longer, a difference much exaggerated in Machilis. In the family Lepismidae the maxillary palpi are long, and the body is clothed with scales.
Machilis polypoda has only been found in Great Britain: it inhabits woods and dry places, is about half an inch long, and is brown in colour, with a metallic lustre. . .
a. Antennae composed of many setose joints, tapering to their extremities and longer than the body. The terminal joints are united in groups of seven.
b. Maxillary palpi composed of six joints. The three terminal joints are recurved. c. Eyes. Simple according to Packard, large and black; contiguous in this genus, but small and widely separate in Lepisma. The above described parts are borne upon the head, which is distinctly marked off from the thorax. The latter consists of three limb-bearing somites as in all Insecta, but it is not distinctly marked off by any constriction from the abdomen which has ten somites.
d. Anterior or prothoracic legs. The prothorax is large and arched.
e. Meso-thoracic, or middle pair, and f. Meta-thoracic, or posterior pair, of limbs.
These limbs in Machilis bear on their basal joints a short cylindrical appendage covered with stiff hairs and closely resembling the cylindrical appendages of the abdomen. The processes in question may be seen projecting in front of the corresponding limbs.
In Scolopendrella, a Myriapod (? Insect) classified by Packard with the Thysanura, there is a similar appendage internal to the bases of each of its twenty-two limbs. It may be noted also that Scolopendrella agrees with Ca?npodea among Thysanura, and with the Collembola in having both mandibles and maxillae sunk in the head.
g. The first of the ten somites composing the abdomen. The ventral surface of each, except the first, bears a pair of setose cylindrical appendages. The last pair is large. They are moved by the animal as it runs.
In Lepisma saccharina these appendages are present only on the last two somites, and are represented on the anterior somites by groups of stiff hairs. In Cam-podea and Iapyx they are absent on the eighth and ninth somites. They appear to represent abdominal legs. Such legs are present in many embryonic Insects, and in larval Lepidoptera, Tenthredinidae, and Panorpatae are developed into prolegs on more or fewer of the abdominal somites. It may be noted that in Machilis the female possesses, in addition apparently to the abdominal limbs, two appendages, on the eighth and ninth somites, which form an ovipositor. As there is no reason to doubt the homology of these processes with the parts of the ovipositor similarly found in many other female Insecta, their homology with limbs appears doubtful, and in need of further elucidation.
h. Median and i. Lateral caudal filaments belonging to the tenth somite. The lateral filaments are perhaps homologous with the abdominal limbs present on the foregoing somites. j. Last and elongated pair of abdominal limbs.
Anatomy of a Collembolan. Sommer, Macrotoma plumbea, Z. W. Z. xli. 1885.
FIGS. 2-4. Mouth-parts of a Tiger-beetle, Cicindela littoralis. From Stein's figures in Carus, Icones Zootomicae, I, Leipzig, 1857, Pl. XIV. Figs. 12-14.
Fig. 1. The mandible, which consists, as in all Insecta, of a single piece. In this carnivorous biting animal, it is curved, pointed, and its inner edge is produced into four sharp teeth.
Fig. 3. The maxilla composed of six parts.
a. The lacinia with a terminal hook which is moveably articulated, and distinguishes, among other points, the small family Cicindelidae or Tiger Beetles from the large family Carabidae or Ground Beetles.
b. Palpiform two-jointed galea, which is distinctive of the tribe Adephaga, comprising the families Cicindelidae, Carabidae, Dyticidae, and Gyrinidae among the Coleoptera Pentamera.
c. The four-jointed maxillary palp, articulated to f. The palpiger. This in its turn rests upon e. The stipes and d. The cardo, which articulates with the skull.
Fig. 4. The labium. It is much simplified as compared with the labium in Periplaneta. It consists of a transverse basal piece with two notches in the anterior border separated by a pointed process, and represents, according to Professor Westwood, the mentum. Two four-jointed labial palpi are inserted in the notches. They are described by the authority quoted as three-jointed, with a moveable base. It is difficult to homologise with certainty the parts of so modified an organ. It is possible that this mentum may represent more than the part so termed in Periplaneta.
Cicindelidae. See Westwood, Introduction to Modern Classification of Insects, vol. i. p. 47, 1839.