ON THE BRITISH ANNELIDA. 223 



correlative " simplicity " in the composition of \he fluids. If the solids are 

 reduced in their standard of organization, it follows that the fluids are re- 

 quired to be less elaborately prepared, in order to supply these solids with 

 the materials of increase and renewal. If the solids of the Zoophyte or 

 Medusa were complexly structured like those of the human body, the fluids 

 of the Zoophyte, in obedience to the law of correlation now expounded, 

 ■would present the same highly-wrought composition as those of the human 

 body. The position then may be defined as involving a physiological law, 

 that the processes of nutrition are simple in proportion as the animal is low 

 in rank in the zoological scale ; in other words, the fluids and solids are less 

 and less removed from the standard of lifeless, inorganic matter, as the ani- 

 mal nears more and more the primordial link in the zoological chain. 



These general observations will tend to remove the mystery of the absence 

 in inferior organisms of systems of solid parts on which, in the higher, the 

 most important functions devolve. They will also explain why it is that the 

 digestive and circulating systems are fused into and confounded in one 

 common order of channels; that special organs answering to the renal, of the 

 vertebrated animal, do not exist. It is probable, from the very chemical 

 nature of the inferiorly organized fluids of the lower grades in the inverte- 

 brate series, that there may exist in these fluids no urea to be removed ; a 

 renal apparatus would therefore prove superfluous and unnecessary. A 

 separate order of gastric glands, supplying an acid fluid, may not exist in 

 the Annelida, because that description of change which such a product is 

 fitted to impress on the food, may not be required in order to its conversion 

 into their blood*. 



This subject deserves the deepest study of the physiologist. It is obviously 

 pregnant of valuable results. The real question is, whether the same organ, 

 homologously, in the animal series produces the same secretion chemically, 

 capable of doing the same work and no other ; for if, for example, the bile 

 of the Annelid does the work, not only of bile, but also of gastric juice, then 

 it follows, that, although the gland producing this fluid in the Annelid may 

 be homologous with the liver of the higher animals, the secretion furnished 

 by that gland is not the correlate of that afforded by the liver of the higher 

 animals. Within the province of human physiological anatomy, it may indeed 

 be argued, that although it may be proved by dissection that the group of 

 salivary glands constitute truly one homogeneous apparatus, the parts of 

 which bear by their texture a perfect analogy to each other, yet that physio- 

 logical analysis and chemical experiments, on the contrary, by pointing out 

 the diversity of the secreted fluids, and by causing the observer to notice the 

 nervous force which regulates the secretions, teach us that each gland pre- 

 sides over one special act, and that, although the structure may be the same, 

 the functions are performed under the agency of distinct and independent 

 influences. It cannot, for instance, at present be disputed, that although the 

 different kinds of saliva are poured into the mouth simultaneously, their use 

 remains nevertheless distinct; and experience proves that the principal 

 function of the parotid gland is to secrete a fluid which is to favour masti- 

 cation, that of the sub-maxillary gland for gustation, and of the sub-lingual 

 gland and buccal follicles for deglutition. It is only by the assistance of 

 these physiological data that the modifications which the salivary organs 

 undergo in the different classes of vertebrated animals can be studied and 

 understood according to their true meaning. The characters of salivary 

 glands are not to be deduced from their anatomical structure, their volume 



* M. Bernard has recently, I find, read a paper before the Academy of Sciences of Paris, 

 on the very points to which attention is drawn in the text. 



