CHAP. XL] OF ALIMENTATION IN GENERAL. 173 



even the bivalvous mollusks, are forced to content themselves 

 with sucking in the dissevered organic molecules as these pass 

 along, or sometimes the animal cula, which the aqueous medium 

 brings them. Some aid chance by causing a current of water to 

 pass incessantly into their digestive cavities. 



In short, most invertebrated animals live upon animal sub- 

 stances, excepting always the majority of insects ; but these 

 latter have moreover a complete digestive system, already 

 differentiated, at the adult age. In the state of larvae, on the 

 contrary, they often feed upon animal matters. Fish, and even 

 reptiles, are also, for the most part, carnivorous. We must 

 come to birds and to mammifers to find important groups of 

 animal species, living habitually upon vegetals. 



A general fact, strange at first sight, arises out of the com- 

 parative examination of the digestive system in marine herbivora, 

 whatever may be their place in the animal hierarchy. In effect, 

 in the tsrrestrial animals, the herbivorous digestive tube is more 

 differentiated, more complex, furnished with gastric, pouches, 

 with csecums vaster and more numerous than the carnivorous 

 digestive tube possesses. The porcupine has as many as fourteen 

 stomachic cavities. * Now we observe precisely the contrary in 

 aquatic animals, in which we see herbivorous alimentation 

 generally coinciding with a simplified digestive system. Thus 

 in the herbivorous cyprinus there is not even any stomachal 

 distention ; and it is the same in the tadpole. The cetaceous 

 herbivora (the lamentine, dugong, &c.) have only one stomach 

 with simple or double dilatation, while the cetaceous carnivora, 

 (dolphin, whale, &c.) have three, four, five stomachs, and tho 

 squalus peregrimc* many stomachal cavities. 



The explanation of this anatomical paradox seems to us easy 

 to give. The general principle is, not that every herbivorous 

 animal must have a more complex stomach, but that every 

 animal must possess a digestive system more differentiated in 

 proportion as its alimentation is more varied ; now, in the 

 1 J. W. Draper, Human Physiology, &c., p. 59. 



