474 NOTES 



80 The " tusks " of the elephant are prolonged incisors ; those of the 

 walrus, wild boar, and narwhal are canines. 



81 " I was one day talking with Professor Owen in the Hunterian Mu- 

 seum, when a gentleman approached, with a request to be informed respect- 

 ing 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 examination, Owen quietly remarked, ' That is the third molar 

 of the under jaw of an extinct species of rhinoceros.' " LEWES'S Studies 

 in Animal Life. 



82 This gap or interspace, so characteristic of the inferior mammals, is 

 called diastema. It is wanting in the extinct anoplotherium, is hardly 

 perceptible in one of the lemurs, and is not found in man. 



83 In the spermaceti whale, the teeth are fixed to the gum. 



84 The iguana among reptiles, and fishes with pavement teeth, approach 

 the mammal in this respect. 



85 This movement is called peristaltic or vermicular, and characterizes 

 all the successive movements of the alimentary canal. 



86 Fishes and amphibians have no saliva, but a short gullet. Birds are 

 aided by a sudden upward jerk of the head. 



87 Fishes and reptiles have no pharynx proper, the nostrils and glottis 

 opening into the mouth. 



88 This movement of the pharynx and esophagus is wholly involuntary. 

 Liquids are swallowed in exactly the same way as solids. 



89 The few animals in which the digestive cavity is wanting are called 

 agastric, and agree in having a very simple structure. Such are some 

 Entozoa (as tapeworm) and unicellular Protozoa (as Gregarina}. They 

 absorb the juices, already prepared, by the physical process of endosmose. 

 There are other minute organisms (bacteria) which seem to be able to ex- 

 tract the necessary elements, C H O N, from the medium in which they live. 



90 The cavity of a sponge is perhaps homologous with the digestive 

 cavity, but is not functionally such. Each cell lining it does its own 

 digestion, taking the food from the water circulating in the cavity. 



91 " Nothing is more curious and entertaining than to watch the neat- 

 ness and accuracy with which this process is performed. One may see the 

 rejected bits of food passing rapidly along the lines upon which these 

 pedicellariae occur in greatest number, as if they were so many little roads 

 for the conveying away of the refuse matters ; nor do the forks cease from 

 their labor till the surface of the animal is completely clean and free from 

 any foreign substance." AGASSIZ'S Seaside Studies. 



92 In the larva of the bee, the anal orifice is wanting. 



93 The length of the canal in insects is not so indicative of the habits as 

 in mammals. Thus, in the carnivorous beetle the canal is nearly as long 

 as, and more complicated than, it is in the nectar-sipping butterflies. 



94 The object of this is unknown. It does not occur in the oyster. 



