The Long Spiders (Arthrogastres), in which the earlier articulation of body has been better preserved than in Round Spiders, appear to be the older and more original forms. The most important members of this sub-class are the scorpions, which are connected with the Solifugæ through the Tarantella (or Phrynidæ). The small book scorpions, which inhabit our libraries and herbariums, appear as a degenerate lateral branch from the true scorpions. Mid-way between the Scorpions and Round Spiders are the long-legged Tailor-spiders (Opiliones) which have possibly arisen out of a special branch of the Solifugæ. The Pycnogonida, or No-body Crabs, and the Arctisca, or Bear Worms—still generally included among Long Spiders—must be completely excluded from the class of Spiders; the former belong to the Crustacea, the latter to Ringed worms.
| SYSTEMATIC SURVEY | |||||||
| Of the 3 Classes and 17 Orders of the Tracheata. | |||||||
| Classes of Tracheata. | Sub-classes of Tracheata. | Orders of Tracheata. | Two Names of Genera as examples. | ||||
| I. Spiders Arachnida |
| I. Long spiders Arthrogastres |
| 1. | Scorpion spiders Solifugæ |
| Solpuga Galeodes |
| 2. | Tarantella Phrynida |
| Phrynus Thelyphonus | ||||
| 3. | Scorpions Scorpioda |
| Scorpio Buthus | ||||
| 4. | Book scorpions Pseudoscorpioda |
| Obisium Chelifer | ||||
| 5. | Tailor spiders Opilionida |
| Phalangium Opilio | ||||
| II. Round spiders Sphærogastres |
| 6. | Spinning spiders Araneæ |
| Epeira Mygale | ||
| 7. | Mites Acarida |
| Sarcoptes Demodex | ||||
| II. Centipedes Scolopendria or Myriapoda |
| III. Simple-footed Chilopoda |
| 8. | Simple-footed Chilopoda |
| Scolopendra Geophilus |
| IV.Double-footed Diplopoda | 9. | Double-footed Diplopoda |
| Julus Polydesmus | |||
| III. Flies Hexapoda |
| V. Chewing Masticantia |
| 10. | Primitive flies Archiptera |
| Ephemera Libellula |
| 11. | Gauze-wings Neuroptera |
| Hemerobius Phryganea | ||||
| 12. | Straight-wings Orthoptera |
| Locusta Forficula | ||||
| 13. | Beetles Coleoptera |
| Cicindela Melolontha | ||||
| 14. | Bee-wings Hymenoptera |
| Apis Formica | ||||
| VI. Sucking Sugentia |
| 15. | Bugs Hemiptera |
| Aphis Cimex | ||
| 16. | Two-wings Diptera |
| Culex Musca | ||||
| 17. | Butterflies Lepidoptera |
| Bombyx Papilio | ||||
PEDIGREE OF TRACHEATA
| Butterflies Lepidoptera | Isopoda | |||||
| Bees Hymenoptera | | │ │ | Two-wings Diptera | | ||
| │ | │ | │ | ||||
| Beetles Coleoptera | │ │ | | │ │ | │ │ | Bugs Hemiptera | |
| │ | │ | │ | │ | │ | ||
| │ |
| │ | │ | |||
| Straight-wings Orthoptera | Gauze wings Neuroptera |
| ||||
| │ | │ | │ | ||||
| ||||||
| Primæval Flies Archiptera | ||||||
| Scorpions Archiptera | │ │ | Double-footed Diplopoda | ||||
| Tailor Spiders Opiliones | │ │ | │ │ | │ │ | |||
| │ │ | Book Scorpions Pseudoscorpioda | │ │ | │ │ | │ │ | ||
| Mites Acarida | │ │ | │ │ | │ │ | │ │ | │ │ | |
| │ | │ |
| │ | │ | ||
| │ │ | │ │ | Tarantella Phrynida | │ │ | │ │ | ||
| Weaving Spiders Araneæ │ │ | │ │ │ │ | │ │ │ │ | │ │ │ │ | Simple-footed Chilopoda Centipedes Myriapoda | ||
| │ | │ | ||||
| Scorpion Spiders Solifugæ Spiders. Arachnida | │ │ │ │ | │ │ │ │ | ||||
| │ │ | Flies. Insecta Hexapoda | │ │ | ||||
| │ | │ | │ | ||||
| ||||||
| Primary Air-breathing Arthropods Protracheata | ||||||
| │ | ||||||
| Articulated Worms Coelminthes | ||||||
Fossil remains of Long Spiders are found in the Coal. The second sub-class of the Arachnida, the Round Spiders (Sphærogastres), first appear in the fossil state in the Jura, that is, at a very much later period. They have developed out of a branch of the Solifuga, by the rings of the body becoming more and more united with one another. In the true Spinning Spiders (Araneæ), which we admire on account of their delicate skill in weaving, the union of the joints of the trunk, or metamera, goes so far, that the trunk now consists of only two pieces, of a head-breast (cephalo-thorax) with jaws, feelers, and four pairs of legs, and of a hinder body without appendages, where the spinning warts are placed. In Mites (Acarida), which have probably arisen by degeneration (especially by parasitism) out of a lateral branch of Spinning Spiders, even these two trunk pieces have become united and now form an unsegmented mass.
The class of Scolopendria, Myriapoda, or Centipedes, the smallest and poorest in forms of the four classes of Arthropoda, is characterized by a very elongated body, like that of a segmented Ringed worm, and often possesses more than a hundred pairs of legs. But these animals also originally developed out of a six-legged form of Tracheata, as is distinctly proved by the individual development of the millipede in the egg. Their embryos have at first only three pairs of legs, like genuine insects, and only at a later period do the posterior pairs of legs bud, one by one, from the growing rings of the hinder body. Of the two orders of Centipedes (which in our country live under barks of trees, in moss, etc.) the round, double-footed ones (Diplopoda) probably did not develop until a later period out of the older flat, single-footed ones (Chilopoda), by successive pairs of rings of the body uniting together. Fossil remains of the Chilopoda are first met with in the Jura period.