ASSIMILATING GLANDS ABSORPTION IN INVERTEBRATA. 201 



224. There are certain glandular bodies, disposed in various 

 parts of the system, which seem to discharge a similar office ; 

 withdrawing the raw material (so to speak) from the general 

 current of the circulation, and returning it again in a state of 

 higher elaboration. Such are the Spleen, the Thyroid and 

 Thymus glands, and the Supra-Eenal capsules. Besides these, 

 the Liver probably exerts an assimilating action upon the crude 

 materials which are made to pass through its substance, almost 

 immediately after having been received into the blood-current, 

 and before they are allowed to pass into the general circula- 

 tion ; the whole of the blood returned by the gastric and 

 mesenteric veins from the walls of the alimentary canal, being 

 conveyed through the liver by the portal system, in its way to 

 the heart ( 267). 



225. In the Invertebrated animals, neither lacteals nor 

 lymphatics exist; and the blood-vessels, whose absorbent 

 powers are to a certain extent restricted in the higher animals, 

 have to perform the functions of these. There are animals, 

 however, which are destitute not only of lacteal and lymphatic 

 vessels, but even of blood-vessels ; and in these, as in the 

 Cellular Plants, there is but little transmission of fluid from one 

 part of the body to the other ; for every portion, both of the 

 internal surface (or lining of the stomach), and of the external 

 surface which is bathed in the surrounding fluid (for most of 

 these animals are aquatic), seems equally to possess the power 

 of absorption ; and the parts to whose nourishment the fluid 

 thus received into the body is to be appropriated, are in the 

 immediate neighbourhood of those which have absorbed it. 

 This is the case, for example, in the Hydra and Sea- Anemone, 

 and, more or less, in all the Polypes ; as well as in the lower 

 "Worms. Between these, therefore, and the Cellular Plants, a 

 remarkable analogy exists in regard to the mode in which the 

 nutriment is absorbed and applied ; the difference being, that 

 the Animal possesses a digestive cavity, lined by an inward 

 extension of the external surface, which does not exist in 

 Plants ( 8). And it is upon the walls of this cavity, that 

 the absorbent vessels of the higher Animals (whether lacteals 

 or blood-vessels) are distributed, collecting the nourishment 

 in contact with them ; just as the roots of a Plant, spread 

 through the soil, draw up that which it contains. But among 

 those lowest animals in which the digestive cavity altogether 



