208 Mr. W. S. Kent on the Relationship of 



equivalent to the operation of feeding in the higher classes of 

 animals. By experiments with finely comminuted indigo 

 placed in the water at such times, he observes that the mole- 

 cules arc rapidly drawn into the pores ; and having undergone 

 digestion in the sarc(ide lining of the interior of the sponge, the 

 efiete matter is ejected through the osculum. The ftecal 

 matters discharged by the oscula, he adds, exhibit all the 

 characteristics of having undergone a complete digestion ; 

 and whatever may have been the condition of the molecules 

 of organized matter on entering the sponge, their appearance 

 after their ejection is always that of a state of thorough 

 exhaustion and collapse. 



The foregoing facts amply demonstrate that a fully organized 

 sponge is entirely dependent on ciliary action for its nourish- 

 ment, and that the nutritious matters on which it subsists are 

 brought to it through numerous apertures, and through the 

 medium of a more or less complex canal-system. 



Referring, now, to fig. 3, as illustrative of our second class, 

 the Zoantharia, it Avill be easy to ascertain the value of the 

 analogies of structure already noticed. 



The terminal orifice, a, is here the sole aperture essential to 

 the well-being of the animal. It constitutes a true buccal ori- 

 fice or mouth, through which all nutrient matters have to pass 

 to the common digestive cavity with its prolongations, c, d, 

 through the medium of the alimentary cavity or canal, b, and 

 through which again, after undergoing digestion, all efiete 

 matters are finally ejected. 



This alimentary system is something totally different from 

 what has just been shown to obtain in Sj^ongilki ; and com- 

 parison of the means l)y which the food is here brought into 

 relationship with tlie digestive cavity reveals at once how 

 essentially and insuperably the two classes are isolated from 

 each other now, however close might have been their bond of 

 affinity in by-gone epochs. In the sponge, ciliary action has 

 been demonstrated to be the highest force exerted for securing 

 the necessary sustenance for its body-mass. This force 

 exerted, as I shall presently show tliere is great reason for 

 believing, is a purely mechanical and involuntary one ; l)ut 

 any one who has watched an Actinia take its food must have 

 recognized that it achieves its end by the exercise of a force 

 incomparably higher than that produced by the action of cilia, 

 its prey, often living creatures almost equalling itself in 

 dimensions, being seized and forcibly dragged, by aid of its 

 tentacles and its prehensile, and frequently protrusible, lips 

 which bound the aperture of the mouth, into its alimentary 

 canal, from which it is passed on to the common digestive cavity. 



