176 BIOLOGY. [BOOK TI. 



Moreover, animal species very closely connected in the tax- 

 inomy differ in their mode of alimentation. The polypi, like 

 most inferior animals, usually feed exclusively upon animal 

 matters. Even the hydras habitually reject vegetal substances, 

 which their rudimentary organization does not permit them to 

 assimilate \ but the tiibularia gelatinosa nevertheless feeds upon 

 the flowers and seeds of the water lentil. 



Among the coleoptera, the plantigrades, and the cetaceans, 

 certain kinds are carnivorous, and others of the same group are 

 herbivorous, &c. 



We have already said above that during abstinence every 

 animal becomes carnivorous. It consumes its own tissues, an<fi 

 even its stomach becomes charged, at the expense of these tissues, 

 with a carnivorous gastric juice, destined for the absent aliments 

 (L. Corvisart). 



Before concluding this very incomplete sketch, it will not be 

 useless to say a few words on geophagy. 



The earth-worms, the naids, swallow the humus of the soil ; , 

 this humus- is kneaded by a kind of musculous gizzard, probably 

 diluted with a secretion, and the residuum is rejected in pulpy 

 cords. According to Swammerdam, the larva of the ephemeris 

 eats clay only. Its colour even varies with the colour of the 

 clay. 



Among the lower beings, geophagy easily explains itself. The 

 vegetal humus, which the earth-worms eat, the moist clay, which 

 the larvae of the ephemerides also swallow on the banks of the 

 rivers where they live, contain a large quantity of organic detri- 

 tus and of soluble salts, which alone are absorbed. Geophagy is 

 less easily comprehended in man ; nevertheless, independently of 

 pathological cases, there are numerous examples of it. 



The Otomacs eat, or rather ate, every day, a pound and a half 

 of unctuous and ferruginous clay. 



Spix and Martius l have observed analogous cases amongst 

 various tribes on the banks of the Amazon. According to 

 1 Reise in Brasilien, t. II. 



