224 REPORT— 1851. 



or form, but from the nature of the functions to which they are subservient. 

 It would therefore prove a physiological error, such as has been committed 

 by J. F. Meckel, to look for parotid and sub-maxillary glands in birds, as those 

 organs cannot exist; since the two corresponding functions, mastication and 

 gustation, are generally wanting in this class of animals. It is thus clear that 

 the useof all the salivary glands which arefound in birds,should be looked upon 

 as ministering to the only function which with them accompanies the inges- 

 tion of food, viz. deglutition. The thick and viscous fluid which is secreted 

 by the glands of birds has nothing in common with the saliva of the parotid 

 and sub-maxillary glands, and is perfectly analogous to the fluid secreted by 

 the sub-lingual gland and buccal follicles of the Mammalia. The parotid is 

 found in its greatest degree of development in such of the Mammalia as ha- 

 bitually chew dry and hard substances, whilst it becomes atrophied in those 

 which live in water and feed upon moist food, though the salivary glands 

 preserve their normal development with reference to the functions with which 

 they are connected. 



The preceding principles, drawn from considerations resting on the evi- 

 dence of general physiology, will, it is hoped, prove of service in elucidating 

 some of the difficult questions which will arise in the attempt to resolve the 

 true meaning of the gland structures engaged in the alimentary system of the 

 Annelida. 



This class of animals, like all others, is distinguishable into those families 

 which subsist on animal food, and into those which are phytophagous ; in ad- 

 dition to which a smaller group may be recognised, whose food is the fluid 

 medium in which they live, extracting from it when swallowed all that it 

 may contain of matter suitable to their wants. The researches of modern 

 naturalists with reference to the Mollusca, have shown that all the species of 

 the same genus do not always inhabit the same kind of situation ; for in 

 many instances some are found on land, some on fresh water, and others in 

 salt. These researches would throw little light on the habitats of the Anne- 

 lida, since of them it may be stated at once that more than four-fifths of the 

 whole class are inhabitants of the sea and the sea-shore. 



The genus Nais is represented on land and freshwater by one species, 

 the genus Lumbricus, by the familiar Earth-worm ; while the genera, Ilirtido, 

 Hcemopis, Nephelis, Clepsina, Gordius and Planaria are almost entirely 

 land and freshwater in their habitats. With these exceptions it may be 

 stated of the Annelida as a class, that it is exclusively marine. The marine 

 Annelida are again subdivisible into the carnivorous and herbivorous groups ; 

 and these again into minor groups, according to the varieties of these two 

 descriptions of food for which they exhibit an instinctive preference. Of the 

 phytophagous species, many affect particular families of Algte, near high- 

 water mark ; others those restricted to the ebb-line of the tide. The car- 

 nivorous species, as regards their mode of obtaining food, exhibit still more 

 numerous varieties. These may always be distinguished by the conformation 

 of the proboscis and of the alimentary canal. In few cases is it possible to 

 infer the nature of the food of any given worm, merely by the inspection of 

 the contents of the intestinal canal ; it is more practicable to predicate the 

 habits of an Annelid by the general structure of its digestive system in which 

 the proboscis, when present, is included. 



" The disposition of the alimentary canal," says Cuvier, " determines, in a 

 manner perfectly absolute, the kind of food by which the animal is nourished ; 

 but if the animal did not possess, in its senses and organs of motion, the 

 means of distinguishing the kinds of aliment suited to its nature, it is obvious 

 it could not exist." — Cuvier, Comp. Anat. vol. i. p. 55. Trans. It will be 



