22 INTRODUCTION. 
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.—x. Whelks (Buccinum), 
Limpets (Patella), Sea-lemons (Doris), Land-snails 
(Helix), Slugs (Limax). 
Ciass VI. PTEROPODA.—Animal oceanic, swimming by means of 
two wing-like appendages, one on each side of the 
head. Size minute.—Zx. Cleodora. 
Cuiass VII. 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 expelled the water which has been 
used in respiration. An external shell in some, an in- 
ternal skeleton in others.—#x. Calamaries (Loligo), 
Cuttle-fishes or Poulpes (Octopus), Paper-Nautilus 
(Argonauta), Pearly Nautilus (Nautilus). 
VERTEBRATE ANIMALS. 
SuB-KINGDOM VI.—VERTEBRATA. 
Body composed of a number of definite segments arranged longitudi- 
nally or one behind the other. The main masses of the nervous system 
are placed on the dorsal aspect of the body, and are completely shut off 
from the general 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. 
Cuass 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. Pharyngobranchii.—Ex. Lancelet (Amphioxus). 
Order 2. Marsipobranchii.— Ex. Lamprey (Petromyzon), Hag- 
fish (Myxine). 
Order 3. Zeleosti (Bony Fishes).—Zx. Eels (Murzenide), Her- 
rings (Clupeidze), Salmon and Trout (Salmonidze), Cod 
and Haddock (Gadidz), Flat-fishes (Pleuronectide), 
Perch (Percidze), Mackerel (Scomberide). 
Order 4. Ganoidei.—Ex. Bony Pike (Lepidosteus), Paddle-fish 
(Spatularia), Sturgeon (Sturio.) 
Order 5. Llasmobranchit.—Ex. Sharks (Carcharidx), Dog-fishes 
(Scylliadze), Saw-fishes (Pristis), Rays and. Skates 
(Raiidz), 
Order 6. Dipnoi.—Ex. Mud-fish (Lepidosiren). 
