A first book in organic evolution - D. Kerfoot Shute

Class 1.—Platyhelminthes: Flat-worms.
Class 2.—Nemathelminthes: Round-worms.
Class 3.—Rotatoria: Rotifer.
Class 4.—Bryozoa.
Class 5.—Brachiopoda: Lampshells.
Class 6.—Nemertina.
Class 7.—Enteropneusta: Balanoglossus.
Class 8.—Gephyrea: Star-worms.
Class 9.—Annulata: Earth-worms, Leeches, Sea-worms.

Branch VI.—Arthropoda. Animals with bilateral symmetry. Bodies segmented, but not uniformly so. Several or all of the segments bear paired jointed appendages variously modified. Chitinous exoskeleton. Digestive canal beneath the heart. Supra-œsophagel ganglion (“brain”) connected by a nerve ring round the gullet with a double chain of ventral ganglia. Cœlome small in the adult. Sexes almost always separate. Often some metamorphosis.

Class 1.—Crustacea: Trilobites, Shrimps, Crabs.
Class 2.—Arachnida: Spider, Scorpion.
Class 3.—Onychophora: Peripatus.
Class 4.—Myriapoda: Centipede.
Class 5.—Insecta: Cockroach, Ants, Butterfly.

Branch VII.—Mollusca. Unsegmented animals, possessing, fundamentally, a bilateral symmetry. A very characteristic structure is the “foot”—a muscular protrusion of the ventral surface. Typically, a projecting fold from the dorsal surface of the body forms a mantle, or pallium; the mantle often secretes a single or double shell covering the viscera. The mantle and shell may both be absent. The central nervous system consists of paired ganglia with connecting commissures, viz.: cerebral, pleural, pedal, and visceral ganglia. Heart possesses two auricles and one ventricle. Respiration generally by gills. Frequently there are two larval stages. Development is often direct.

Class 1.—Lamellibranchiata: Clam, Oyster.
Class 2.—Scaphopoda.
Class 3.—Gasteropoda: Snail, Whelks, Slugs.
Class 4.—Amphineura: Chitons.
Class 5.—Cephalopoda: Squids and Cuttlefish.

Branch VIII.—Vertebrata or Chordata. Vertebrates are animals having a distinct body cavity (cœlome) and a segmental arrangement of parts. A hypoblastic skeletal notochord is always present in the embryo, but tends to be replaced by an axial skeleton of mesoblastic origin (backbone). Gill slits are always present in the embryo and may or may not persist in adult life. Gill-lamellæ do not occur above Amphibians. Heart is ventral. Central nervous system is dorsal. Eye begins to develop as an outgrowth from the brain.

Class 1.—Tunicata.
Class 2.—Leptocardii.
Class 3.—Marsipobranchii.
Class 4.—Pisces.
Class 5.—Amphibia.
Class 6.—Reptilia.
Class 7.—Aves.
Class 8.—Mammalia.

Class 1.—Tunicata. The tunicates are remarkable animals, and seem to stumble on the border line between Invertebrates and Vertebrates. Their vertebrate characteristics—gill slits, notochord, dorsal nervous system, and brain eye—are generally discernible only in the free-swimming larval state. They generally degenerate as they progress towards the adult condition, and diverge greatly from the vertebrate type. They are mostly stationary. They are multicellular animals possessing bilateral symmetry. The body is enveloped by a thickened cuticle containing cellulose. The pharynx, perforated with the gill slits, is surrounded by a peribranchial chamber (atrium) which communicates with the exterior by an atrial opening. Heart is simple and tubular. The nervous system is generally reduced to a single ganglion. Nephridia are absent. Hermaphrodites. Usually a metamorphosis.

Class 2.—Leptocardii. Simple, worm-like vertebrate animals represented by a single distinct type—amphioxus or lancelet. The central nervous system consists of a spinal cord, and a very ill-defined, rudimentary brain. No skeleton other than an unsegmented and persistent notochord which projects beyond the anterior end of the nerve cord. No scales. Gill slits are very numerous in the adult. Amphioxus is widely removed from the fishes by the absence of skull, jaws, definite brain, sympathetic nervous system, ear, eye, genital ducts, spleen, and definite heart, the latter being simple and tubular. No pectoral or pelvic limbs (fins). Blood colorless; gastrula ciliated and free-swimming. Metamorphosis.