THE CHAIN OF SPECIES, 469 



some failure to grow at a certain spot, while the balance of the creat- 

 ure continues its development, until a wall arises around the con- 

 striction and becomes permanent, further growth only increasing the 

 introversion — precisely such a process as we may witness at the hands 

 of a potter when he places a ball of clay upon his wheel. First he 

 flattens the top of his ball; then, as he continues to press upon the 

 point, the adjacent clay rises around it ; and next you have a cup. 

 And such a cup-like cell is the type of all endothentic creatures ; that 

 is, of all animals. 



Naturalists, it is true, regarding only flagrant forms, confine the 

 term coeUnterate to one class ; those that are permanently open-cupped. 

 But, strictly, all differentiate a part of the investing tegument into a 

 cup, for the purpose of carrying about their nutrition ; and, however 

 much the cup may be extended and contorted — drawn out into a tube 

 and folded away into some convenient receptacle, and puckered, and 

 tucked, and furnished with a thousand little pockets supplementary — it 

 is all but an extension of that same original internal fold or cup. Fi- 

 nally, in the highest animals, all the principal vital functions are found 

 severally the office of some pocket of the integument involuted and 

 shoved out of sight and out of harm's way into the great cavity. 



Having obtained for our animal kingdom the cupped cell as a type, 

 we have plain sailing for some time. 



In the outset, we may subdivide the kingdom into the occaslonallij 

 cupped and the perincmently cupped. Those that present the cup as 

 occasion serves, or only in one stage of their evolution, are exemplified 

 in the Khizopoda. The permanently-cupped include not only those 

 always open-mouthed — the coslenterata of Mr. Huxley — but, as we have 

 seen, necessarily all of the higher classes. 



Observe, again, the India-rubber ball. First, we have the cup. 

 Xow, this open cup is mouth — is stomach — is vent — is every thing. 

 Every thing that goes into the creature enters here ; all that comes out 

 finds exit by means of this common gap. Soon Nature, so to speak, 

 finds this plan poor economy, and divides off" one side, or edge of the 

 cup, for one purpose, another for another purpose, and we find one 

 corner or edge of it devoted to the entrance of nutrition, another to 

 the exit of the debris. Nor is this mere speculation. Creatures are 

 actually so constituted, and are seen to develop to this type from the 

 ovum. We often see, in coelenterates, as in sea-anemone, a tendency to 

 the same thing. Now, this very fact of voiding indlgesta at one angle 

 of the mouth, while the other is receiving a fresh supply of food, pro- 

 duces a constriction in the unused middle region ; and the consequence 

 is that here the lips approximate one another, and finally, adhering at 

 the point of contact, a \)QYvci'.\uQ\\t 2'>&rm(ieun%-U7ce septum is formed. 



This adhesion completed, nothing more is wanting to exhibit the 

 type of the higher anhnalla j for here is a complete alimentary canal, 

 however short, and a dorsal and a ventral aspect. This is an animal 



