The History of Creation, Vol. 2 (of 2) / Or the Development of the Earth and its Inhabitants by the Action of Natural Causes

by Ernst Haeckel

PEDIGREE OF GILLED INSECTS.

	Brachyura						Isopoda
	│					Læmodipoda	│
	Anomura					│	│
	│					Amphipoda	│
	│					│	│
	Macrura	Stomatopoda
	Decapoda	│				Cumacea
	│	│				Edriophthalma
	│	│				│
						│
	│					│
				chizopoda Podophthalma
				│
				Zoëpoda Malacostraca
	Gigantostraca			│			Rhizocephala
	│			│			│
	│			│	Siphonostoma		│
	│ │	Xiphosuræ		Zoëa	│ │		Cirripediæ Pectostraca
	│	│		│	│		│
	│	│		│	│		│
				│	│		│
	Pœcilopoda			│	│		│
	│		Nebaliæ	│	│		│
	│ │		│ │	│ │	Eucopepoda Copepoda		│ │
	Belinurœ		│ │	│ │	│ │		│ │	Pycnogonida Pantopoda
	│		│	│	│		│	│
	Trilobita		│	│	│		│	│
	│		Phyllopoda		│	Ostracoda	│	│
Cladoceræ	│		│		│	│	│	│
│	│		│		│	│	│	│
					│			│
Branchiopoda					│	│		│
│					│	│		│
	Nauplius
	│
	Archicaridæ
	(Articulated Worms)

The pedigree on p. [177] will show how we may at present approximately conceive the derivation of the twenty orders of Crustacea enumerated on p. [176], from the common primary form of the Nauplius. Out of the Nauplius form—which originally existed as an independent genus—the five legions of lower Crabs developed as diverging branches in different directions, which in the systematic survey of the class are united as Segmented Crabs (Entomostraca). The higher division of Mailed Crabs (Malacostraca) have likewise originated out of the common Nauplius form. The Nebalia is still a direct form of transition from the Phyllopods to the Schizopods, that is, to the primary form of the stalk-eyed and sessile-eyed Mailed Crabs. The Nauplius at this stage gives rise to another larva form, the so-called Zoëa, which is of great importance. The order of Schizopoda, those with cloven feet (Mysis, etc.), probably originated from this curious Zoëa; they are at present still directly allied, through the Nebalia to the Phyllopoda, those with foliaceous feet. But of all living crabs the Phyllopods are the most closely allied to the original primary form of the Nauplius. Out of the Schizopoda the stalk-eyed and sessile-eyed Mailed Crabs, or Malacostraca, developed as two diverging branches in different directions: the former through shrimps (Peneus, etc.), the latter through the Cumacea (Cuma, etc.), which are still living and closely allied to the Schizopoda. Among those with stalked eyes is the river crab (cray-fish), the lobster, and the others with long tails, or the Macrura, out of which, in the chalk period, the short-tailed crabs, or Brachyura, developed by the degeneration of the tail. Those with sessile eyes divide into the two branches of Flea-crabs (Amphipoda) and Louse-crabs (Isopoda); among the latter are our common Rock-slaters and Wood-lice.

The second main-class of Articulated animals, that of the Tracheata, or air-breathing Tracheate Insects[4] (Spiders, Centipedes, and Flies) did not develop until the beginning of the palæolithic era, after the close of the archilithic period, because all these animals (in contrast with the aquatic crabs) are originally inhabitants of land. It is evident that the Tracheata can have developed only after the lapse of the Silurian period when terrestrial life first began. But as fossil remains of spiders and insects have been found, even in the carboniferous beds, we can pretty accurately determine the time of their origin. The development of the first Tracheate Insects out of gill-bearing Zoëa-crabs, must have taken place between the end of the Silurian and the beginning of the coal period, that is, in the Devonian period.

Gegenbaur, in his excellent “Outlines of Comparative Anatomy,”[(21)] has lately endeavoured to explain the origin of the Tracheata by an ingenious hypothesis. The system of tracheæ, or air pipes, and the modifications of organization dependent upon it, distinguish Flies, Centipedes, and Spiders so much from other animals, that the conception of its first origin presents no inconsiderable difficulties to phylogeny. According to Gegenbaur, of all living Tracheate Insects, the Primæval Flies, or Archiptera, are most closely allied to the common primary form of the Tracheata. These insects—among which we may especially mention the delicate Day flies (Ephemera), and the agile dragon-flies (Libellula)—in their earliest youth, as larvæ, frequently possess external tracheate gills which lie in two rows on the back of the body, and are shaped like a leaf or paint-brush. Similar leaf or paint-brush shaped organs are met with as real water-breathing organs or gills, in many crabs and ringed worms, and, moreover, in the latter as real dorsal appendages or limbs. The “tracheate gills,” found in the larvæ of many primæval winged insects, must in all probability be explained as “dorsal limbs,” and as having developed out of the corresponding appendages of the Annelida, or possibly as having really arisen out of similar parts in Crustacea long since extinct. The present tracheal respiration of the Tracheata developed at a later period out of respiration through the “tracheate gills.” The tracheate gills themselves, however, have in some cases disappeared, and in others become transformed into the wings of the Flies. They have disappeared entirely in the classes of Spiders and Centipedes, and these groups must accordingly be conceived of as degenerated or peculiarly developed lateral branches of the Fly class, which at an early period branched off from the common primary form of Flies; Spiders probably did so at an earlier period than Centipedes. Whether that common primary form of all Tracheata, which in my General Morphology I have named Protracheata, did develop directly out of genuine Ringed worms, or at first out of Crustacea of the Zoëa form (Zoëpoda, p. [212]) will probably be settled at some future time by a more accurate knowledge and comparison of the ontogeny of the Tracheata, Crustacea, and Annelida. However, the root of the Tracheata, as well as that of the Crustacea, must in any case be looked for in the group of Ringed worms.

The genuine Spiders (Arachnida) are distinguished from Flies by the absence of wings, and by four pairs of legs; but, as is distinctly seen in the Scorpion-spiders and Tarantulæ, they, like Flies, possess in reality only three pairs of genuine legs. The apparent “fourth pair of legs” in spiders (the foremost) are in reality a pair of feelers. Among the still existing Spiders, there is a small group which is probably very closely allied to the common primary form of the whole class; this is the order of Scorpion-spiders, or Solifugæ, (Solpuga, Galeodes), of which several large species live in Africa and Asia, and are dreaded on account of their poisonous bite. Their body consists—as we suppose to have been the case in the common ancestor of the Tracheata—of a head possessing several pairs of feelers like legs, of a thorax, to the three rings of which are attached three pairs of legs, and of a hinder, body, or abdomen, consisting of many distinct rings. In the articulation of their body, the Solifugæ are therefore in reality more closely related to flies than to other spiders. Out of the Devonian Primæval Spiders, which were nearly related to the Solifugæ of the present day, the Long Spiders, the Tailor Spiders, and the Round Spiders probably developed as three diverging branches.

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

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