PHYSIOLOGY OF THE INVERTEBRATA. 23 



kingdom is that of saprophytic or enclosmosis nutrition. It 

 occurs in the Gm/arinida, &c., and is the simplest type of 

 nutrition, for the organism simply nourishes itself by 

 absorbing, through the whole surface of its body, the liquids 

 containing decomposing or digested animal and vegetal 

 substances. 



The third and highest type of nutrition occurs in all 

 animals except those coming under the previously mentioned 

 types. In the highest type of nutrition the organism 

 '' seizes solid alimentary particles, and nourishes itself after 

 the fashion of an animal, whether it be by means of a 

 permanent mouth, or by means of an adventitious one, 

 improvised at the moment of need." 



Before describing in detail the great physiological functions, 

 it may be stated that " in organised beings, from the lowest 

 to the highest, the most differentiated, there is a graduated 

 hierarchy. From the physiological confusion which exists at 

 the lowest step of the ladder we pass, step by step, through 

 a series of organic models, better and better finished, to the 

 most perfect specialisation. Nothing is more interesting 

 than this seriation of organs, especially from the point of view 

 of the great doctrine of evolution, which more and more 

 vivifies all the branches of natural histoiy." 



The Protozoa. 



(a) The Grcgarina. — This animal (Fig. 2, a) infests the 

 interior of cockroaches, earthworms, and other Invertebrates. 

 It well illustrates an example of endosmosis or saprophytic 

 nutrition, for it absorbs or imbibes fluid nutriment by every 

 part of its surface, and most probably the effete matter is 

 likewise given out at every part of its surface. 



Although the anatomical structure oi the Greg arina giy^B it 

 a higher rank in the zoological scale than the Amccba, the 

 latter organism is certainly its superior in the matter of 

 digestion. It may be stated that the gradual specialisation of 



