370 NOTES. 
26 At one end of the Tape-worm is a minute pore, by some considered the 
mouth, with a circlet of spines and four suckers. 
27 The real tongue forms the floor of the mouth, and is found as a distinct 
part in a few Insects, as the Crickets. 
28 In a few Fishes, it is circular or oval. 
22 The mouth of the Whale is exceptional, the walls not being dilatable. 
The act of sucking is characteristic of all young Mammals, hence the need 
of lips. 
30 The Ant-eater has two callous ridges in the mouth, against which the 
insects are crushed by the action of the tongue. 
31 Strictly speaking, the baleen plates do not represent teeth; for in the 
embryo of the Whale we find minute calcareous teeth in both jaws, which 
never cut the gum. The whalebone is probably a peculiar development of 
hair in the palate, and under the microscope it is seen to be made up of 
fibres which are hollow tubes. 
32 The “tusks” of the Narwhal and Elephant are prolonged incisors ; 
those of the Walrus and Wild Boar are canines. 
33 “¢T was one day talking with Professor Owen in the Hunterian Museum, 
when a gentleman approached, with a request to be informed respecting the 
nature of a curious fossil which had been dug up by one of his workmen. 
As he drew the fossil from a small bag, and was about to hand it for exam- 
ination, Owen quietly remarked, ‘ That is the third molar of the under jaw 
of an extinct species of rhinoceros.’ ’’—LrEwes’s Studies in Animal Life. 
34 This gap or interspace, so characteristic of the inferior Mammals, is 
called diastema. It is wanting in the extinct Anoplotherium, and is hardly 
perceptible in one of the Lemurs. 
35 In the Spermaceti-whale, the teeth are fixed to the gum. 
36 The Iguana among Reptiles, and Fishes with pavement-teeth, approach 
the Mammals in this respect. ‘ 
37'This movement is called peristaltic or vermicular, and characterizes all 
the succeeding movements of the alimentary canal. 
38 Fishes and Amphibians have no saliva, but a short gullet. Birds are 
aided by a sudden upward jerk of the head. 7 
3° Fishes and Reptiles have no pharynx proper, the nostrils and glottis 
opening into the mouth. 
4° This movement of the pharynx and csophagus is wholly involuntary. 
Liquids are swallowed in exactly the same way as solids. 
41 The few animals in which the digestive cavity is wanting are called 
agastric, and agree in haying a very simple structure, and in being parasitic. 
Such are some Entozoa (as Tape-worm), and unicellular Protozoa (as Grega- 
rina). They absorb the juices, already prepared, by the physical process of 
endosmose. There are other minute organisms which seem to be able to 
extract the necessary elements, CHON, from the medium in which they 
live. 
42 Moreover, as a Sponge is an aggregation of animals, these canals are for 
a community, not for a single individual. According to Alexander Agassiz, 
the Ctenophore have a true alimentary canal, passing through the body- 
cavity. 
