THE CHYL AQUEOUS FLUID. 269 



grateful acknowledgment, considers tliat in the Ecliino- 

 derniata the blood-proper first makes its appearance ; 

 below that point there is no blood, but only chyl- 

 aqueous fluid ; and even for several stages higher, this 

 chylaqueous fluid continues to hold its place beside the 

 true blood ; so that a worm, for instance, has two fluids 

 — blood, circulating in a system of closed vessels, and 

 chylaqueous fluid oscillating in the general cavity out- 

 side the vessels.* 



It is indispensable, in philosophic zoology, to dis- 

 criminate between hlood, a fluid of definite constitution 

 circulating in a system of vessels, and the chylaqueous 

 fluid, formed of "water and the products of digestion, 

 oscillating in the general cavity. But my investiga- 

 tions lead to a still further reduction of this latter 

 fluid ; and instead of saying, with Dr Williams, that 

 the simplest condition of a nutrive fluid is a " very 

 dilute solution of albumen in sea water,'' f I am forced 

 by facts to say that lower even than this is the earliest 

 state of the nutritive fluid : namely, sea water carrying 

 certain gases and organic particles, but without deflnite 

 chyle-corpuscles, such as Dr WilKams figures — without 

 even albumen in solution, at least as a constant ele- 

 ment. This is the case with all the Sponges. They 

 simply suck in sea water and expel it. The reader 

 will, however, learn with surprise that this also is the 

 case with the far more highly organised Actinice ; a 



* See page 71. 



t See his paper on "The Blood" in the Brit, and For. Med. Rev., 

 Oct. 1853, p. 4S0. 



