232 THE ORGANIZATION 



former evidently having no sort of relation to the latter, as regards 

 its connection with the other organs, in a functional sense, but 

 purely one of position. Not only is this true of the Lancelot, 

 but also of many other nearly related fishes, such as Lamprey- 

 Eels, Myxine, and certain Sharks; and it is not until, by follow- 

 ing up the series, we arrive among the considerably more elevated 

 forms, that we find the arch completely encircling the nervous 

 cord ; and not even in the whole class of fishes are the successive 

 arches so close together as to lead any one but an over-eager 

 advocate of such a view to conceive that the series of perfora- 

 tions which they enclose are functionally a closed cavity. The 

 open spaces between the successive arches are much wider than 

 the spaces which they enclose, and it is only in the highest an- 

 imals that this proportion is reversed. Yet even in the latter 

 case, the interspaces are by no means closed ones, but are open 

 to a greater or lesser extent to allow the passage of the great 

 lateral nerves (fig. 135, g- 1 , g-' 2 ) which diverge right and left from 

 the main cord (/) and branch through the various organs.* 



The digestive system comprises the mouth, teeth, (e?,) a slender 

 gullet (g-) leading through the diaphragm (dp) to an oval expan- 

 sion, the paunch or stomach, (st,) then contracting in a long, con- 

 voluted intestine (i) which terminates (i l ) at the posterior end 

 of the body. Appended to the fore part of the intestine, just 

 behind the stomach, is the large concavo-convex liver, (y,) and 

 close to it the spleen (s). Near the back are the kidneys, (&,) 

 which filter off the waste fluid of the body, and through slender 

 tubes (ttr) pour it into the bladder (bl). 



* Should any one urge that the vertebral arches embrace what is to all intents 

 and purposes a closed cavity, as contradistinguished from the visceral chamber, 

 and that in the lower Vertebrates the mere rudiments of the arches are sufficient 

 indications of the universal presence of such a cavity, I am willing to admit the 

 truth of the assertion, provided that I may claim at the same time that the car- 

 tilaginous box of the head of Cephalopoda, and the more or less complete arches 

 which border the main nervous cord of Insects, form what is essentially a similar 

 segregated cavity. The basis of difference between the Vertebrata and the 

 other grand divisions lies in the notoc/tonl, and not in the presence of an imagi- 

 nary upper and lower cavity. 



