The stigma in Diplopoda and in Scutigera leads into a chamber or 'tracheal sac,' from which originate bundles of simple tracheal tubes. Glomeris, however, is an exception. Each of its tracheal sacs gives origin to two branching trunks. Large tracheae, which branch and anastomose both longitudinally and transversely, arise from each stigma in Chilopoda a group in which the lining cuticle and spiral line are well marked. It is possible that the Archipolypoda possessed a pair of branchial appendages, situated ventrally on each somite. A single pair of urinary or Malpighian tubes opens into the proctodaeum in Diplopoda, two pairs in Chilopoda.

1 One of the English Scolopendridae discharges a phosphorescent fluid on irritation. Some Chilopoda possess two phosphorescent spots upon the head (Belt, Naturalist in Nicaragua, 1874, p. 141).

2 The corneal hypodermis (= vitreous cells) is perhaps always present in development. The horizontal position of the visual rods or of those placed near the rim of the cup may be due, as suggested by Patten, either to the collapse of a vesicle through the action of reagents, or to the lamination of a vitreous body. The rods ( = retinidia) of the basal cells in the eye of Lithobius, as figured by Grenadier, appear to be terminal, and to constitute a retineum. The conical vitreous body of Scutigera is probably to be interpreted as a compound retinidium surrounded by several 'circles of retinulae. See Patten's general remarks on the Arthropod eye, pp. 665-6S8, Mittb. Zool. Stat. Naples, vi. 1886; and for significance of terms, p. 492 of this book and the note p. 452. The structure of the Myriapod eye needs re-examination.

3 The Myriapod 'of the division Sugentia' ( = Folyzonidae) 'of Brandt,'mentioned by Belt, op. cit. supra, p. 140, which discharges a viscid fluid over its prey, is a species of Peripatus: see Moseley, A. N. H. (5), iii. 1879, P- 265The sexes are separate. The ovary is generally a single tube, rarely double as in Craspedosoma (Diplopoda). There are two oviducts in Diplopoda, one or two in Chilopoda. Cement glands and receptacula seminis open either into the oviduct itself or, as is more usual, into the genital orifice. The testis also may be a single tube, or as in some Diplopoda (certain Glomeridae and Iulidae) two tubes connected by transverse anastomoses. The vasa deferentia, like the oviducts, may be single or double, and are always provided with accessory glands. In Diplopoda the two genital apertures are in connection with the basal joint of the second or third pairs of limbs. In Chilopoda there is a single posterior aperture. Iidus has a copulatory organ on the seventh post-cephalic somite; Sphaerotherium three pairs of copulatory appendages between the last pair of ambulatory limbs and the anus; and the corresponding organs in Glomeris are similarly placed. The Scolopendridae possess a short penis. Scolopendra is viviparous, other Myriapoda lay their eggs in earth, etc.

The young Paiiropus is hexapodous, so too Lithobius1. Some of the Diplopoda have an hexapodous stage, in which however the three pairs of limbs are not on consecutive somites. The majority of Chilopoda appear to possess the full number of limbs at birth. It may be noted that the embryo of Diplopoda developes one or two (Iulus) cuticular envelopes.

1 Haase states, however, that it has eight limb-bearing somites.

A sound-producing apparatus is found in the Chilopod Eucorybas Crotalus and in Sphaerotheritim. In the former the fourth joints of the last pairs of limbs are expanded and leaf-like, and are rubbed together by the animal. In the latter, ridges on the outer side of the middle joint of the second and in S. retusum also of the first pair of copulatory organs in the male work against sharp points on the inner aspect of the last tergum. There is a limited power of reproducing lost parts of the appendages.

Extinct groups of Myriapoda appear in Carboniferous strata in America. Of these Archipolypoda belonging to the Diplopoda, the Proto-syngnatha to the Chilopoda.

The Myriapoda are divisible into two orders.

1. Diplopoda (Chilognathd)

Body cylindrical or semi-cylindrical, with two pairs of feet to the middle and posterior somites; generative apertures on the basal joints of the second or third pairs of limbs.

2. Chilopoda

Body as a rule flattened dorso-ventrally; a 'basilar segment;' second pair of post-oral limbs forming powerful poison claws; one pair of limbs to each somite.

The two pairs of limbs, two ganglia, two stigmata, etc, to each somite in Diplopoda appear to arise not from fusion but from imperfect division of the somite. Cf. Balfour, Comp. Embryology, i. p. 234.

'Myriapoda,' Moseley, Encyclopaedia Brit. (ed. ix.) xvii. Latzel, 'Die Myrio-poden der Oesterreichisch- Ungarnischen Monarchic,' 2 vols. 1884. Cf. On Morphology of Chilopoda, Haase, Z. A. viii. 1884; and On Myriapoda, Packard, A. N. H. (5), xii. 1883.

Pauropoda, Ryder, American Naturalist, xiii. 1879.

Fossil Myriapoda, Zittel, Handbuch der Palaeontologie, Abth. i. Palaeozologie, ii. pt. 5, 1885.

Anatomy of Sphaerotherium, G. C. Bourne, J. L. S. xix.

Sense organs of Antennae, Bourne, op. cit. supra; von Rath, A. M. A. xxvii 1886; Antennal hairs, Sazepin, Mem. Acad. Imp. St. Petersburgh (7), xxxii. 1884; Sensory cavities, Bourne, op. cit. supra; Tomosvary in Naples Zool. Jahresbericht, 1884, pt, ii. p. 132; in Scutigera, Heathcote, Q. J. M. xxv. 1885; cf. Haase in Schneider's Zool. Beitrage, i. 1885.

Hydrogen cyanide, etc. in Fontaria, Weber, A. M. A. xxi. 1882; Guldensteeden-Egeling, Arch. f. Physiol. (Pfliiger), xxviii. 1882; Cope, American Naturalist, xvii. pt. 1. p. 337, 1883. Sticky Secretion in Glomeris, Dewitz, Biol. Centralblatt, iv. 1884-85.

Pharynx of Scutigera, Haase, op. cit.

Respiratory organs of Chilopoda and Symphyla, Haase, op. cit.

Genital organs and development in Geophilus, Sograf; see Naples Zool. Jahresbericht, 1883. pt. ii. p. 90.

Regeneration of lost parts, Newport, Ph. Tr. 134, 1884.

Scolopendrella ( = Symphyla) is placed by Packard with the Thysanura among Insecta. Its mouth-parts are sunk into the head as in Collembola and Campodea; but there are many discrepancies in the accounts of its anatomy, and at present it is perhaps better to leave its position undefined. There is of course nothing intrinsically improbable in the existence of an Insect with very similar somites and fully developed jointed abdominal limbs. Packard, American Naturalist, xv. 1881; Wood Mason, A. N. H. (5), xii. 1883; Ryder, Proc. Amer. Nat. Soc. Philadelphia, 1881; Grassi, Atti R. Accad. Sc. Torino, xxi. 1885; Latzel, op. cit. supra.