INTRODUCTION. 21 



CLASS II. TUNICATA. Animal simple or compound, enclosed in a leathery 

 or gristly case. An imperfect heart. Ex. Sea-squirts 

 (Ascidia). 



CLASS III. BRACHIOPODA. Animal always simple ; the body enclosed in 

 a bivalve shell. Mouth furnished with two long fringed 

 processes or " arms." Ex. Lamp-shells (Terebratula). 



B. MOLLUSCA PROPER. Nervous system consisting of three principal 

 pairs of ganglia. Heart well developed, consisting of at least two chambers. 



CLASS IV. LAMELLIBRANCHIATA (Bivalve Shell-fish) : No distinct head ; 

 no teeth. Body enclosed in a shell which is " bivalve," or 

 composed of two distinct pieces. One or two leaf-like gills 

 on each side of the body. Ex. Oyster (Ostrea), Scallop 

 (Pecten), Mussel (Mytilus). 



CLASS V. GASTEROPODA. A distinct head and toothed tongue. Shell 

 absent in some, but mostly present, and consisting of a single 

 piece (" univalve "). Locomotion effected by creeping about 

 on the flattened under surface of the body (" foot "), or by 

 swimming by means of a fin-like modification of the same. 

 Ex. Whelks (Buccinum), Limpets (Patella), Sea-lemons 

 (Doris), Land-snails (Helix), Slugs (Limax). 



CLASS YI. PTEROPODA. Animal oceanic, swimming by means of two 

 wing-like appendages, one on each side of the head. Size 

 minute. Ex. Cleodora. 



CLASS YII. CEPHALOPODA. Animal with eight or more arms, placed in a 

 circle round the mouth. Mouth armed with jaws, and a 

 toothed tongue. Two or four plume-like gills. In front of 

 the body, a muscular tube (" funnel ") through which is ex- 

 pelled the water which has been used in respiration. An 

 external shell in some, an internal skeleton in others. Ex. 

 Calamaries (Loligo), Cuttle-fishes or Poulpes (Octopus), 

 Paper-Nautilus (Argonauta), Pearly Nautilus (Nautilus). 



VERTEBRATE ANIMALS. 

 SUB-KINGDOM VI VER TEBRA TA. 



Body composed of a number of definite segments arranged longitudinally 

 or one behind the other. The main masses of the nesvous system are placed 

 on the dorsal aspect of the body, and are completely shut off from the gen- 

 eral body-cavity. The limbs (when present) are turned away from that side 

 of the body on which the main nervous masses are situated, and are never 

 more than four in number. In most cases, a backbone, or "vertebral 

 column," is present in the fully-grown animal. 



CLASS I. PISCES (Fishes). Breathing-organs in the form of gills ; heart 

 usually of two chambers, rarely of three ; blood cold ; limbs, when present, 

 converted into fins. 



Order 1. Pharynyobranchii. Ex. Lancelet (Amphioxus). 



Order 2. Marsipobranchii. Ex. Lamprey (Petromyzon), Hag-fish 



(Myxine). 



Order 3. Teleostd (Bony Fishes). .Ex. Eels (Muraenidae), Herrings 

 (Clupeidaa), Salmon and Trout (Salmonidae), Cod and 

 Haddock (Gadidas), Flat-fishes (Pleuronectidae), Perch 

 (Percidae), Mackerel (Scomberidae). 



