CLASSIFICATION OF ANIMALS. 3 



beings, if Linniisus meant "locomotion," this truly is as striking a 

 characteristic of a large proportion of the Animal Kingdom as the 

 fixed or rooted state is of a still larger proportion of the Vegetable 

 Kingdom : but the vegetative fixity of the individual is a character 

 which advances pretty far into the animal series. Not only are most 

 polypes and a few echinoderms adherent to the place of their growth, 

 but the whole class of cirripedes and some genera both of articulate 

 and molluscous animals, e. g. Serpula and Ostrea, are cemented by 

 their shells as immoveably to the rock on which they grow as are the 

 sea-weeds that float beside them from their adherent base. On the 

 other hand, many microscopic single-celled plants, as well as the cili- 

 ated zoospores or embryos of the Vaucheria* and other algae, and of the 

 sponges, have a more rapid locomotion than some of the polygastric 

 animalcules enjoy ; although in neither case, probably, does it arise 

 from a distinct act of volition. The movements of the oscillatoriae, 

 and the more partial shrinkings of the sensitive-plant from the touch, 

 show that "motion" merely, whether of the whole or of the parts 

 of a living organism, will not determine to which kingdom it belongs. 

 Blumenbach, who appreciated the insufliciency of the psychical cha- 

 racter from "spontaneous motion," adopted an anatomical one: — 

 " Plants absorb their nutriment by means of numerous fibres placed at 

 the lower end of their bodies : animals have a simple opening at their 

 upper or anterior extremity, leading to a capacious bag, into which 

 they introduce their food: "f Boerhaavelj: had long before said that 

 the food of plants was absorbed by external roots, and that of ani- 

 mals by internal roots ; and Hunter's favourite anatomical character 

 for animals was the "mouth and stomach." But the free parasitic 

 genus Gregarina §, with its contractile cell-wall, which is soluble in 

 acetic acid, and many of the freely moving infusoria, have no mouth 

 nor alimentary canal ; and there is nothing that can be properly 

 called "stomach" in the cestoidea. The cellular parenchyme of tape- 

 worms is traversed by canals more analogous in character to those 

 which take the place of the digestive cavity in 'sponges. The sap- 

 vessels, and the whole system of intercellular spaces, with their outlets 

 in the stomata, of plants, exhibit an analogous arrangement. Carbonic 

 acid, the nutritive material in plants, passes through the pores of 

 the elongated canals of the intercellular spaces and is taken into 

 the surrounding cells as formative material ; just as albumen and 

 the hydrates of carbon are introduced by the stomata of the tape- 

 worm into the longitudinal canals, and pass through their pores 

 into the surrounding vacuolse or cells : the same materials, in a 



* V. t VI. p. 4. X CL. p. 64. § VII. p. 10. 



B 2 



