34 
INTRODUCTION. 
circulation ; their respiratory organs are almost always on the surface of the body ; 
the greater number have only a sac without issue, for the whole intestine ; and 
the lowest families present only a sort of homogeneous pulp, endowed with motion and ‘ 
sensibility.* , 
1“ The necessity,” writes Mr. Owen, for a dismemberment of the Radiata of Cuvier, which 
Rudolphi justly calls a chaotic groupfj has been felt, and directly or indirectly expressed, by 
most naturalists and comparative anatomists. J It is impossible, indeed, to predicate a com- 
munity of structure in either the locomotive, excretive, digestive, sensitive, or generative 
systems, with respect to this division, as it now stands in the Regne Animal. * * * ; 
“ Taking the nervous system as a guide, the Radiata of Cuvier will be found to resolve them- 
selves into two natural groups, of which the second differs in the absence or obscure traces of 
nervous filaments from the higher division, in whieh these are always distinctly traceable, 
either radiating from an oral ring, or distributed in a parallel longitudinal direction, according 
to the form of the body. 
‘‘These different conditions of the nervous system are accompanied by corresponding 
modifications of the muscular, digestive, and vascular systems ; and a negative character, appli-|| 
cable to the higher division of Cuvier’s Radiata, may be derived from the generative!^ 
system.”§ ' 
It is only in the lower- organized of these divisions, to which the term 
Acrite Animals {Animalia acrita) 
has been applied by Macleay, also that of Protozoa and Oozoa by Cams (from the 
circumstance of its members being analogous to the ova or germs of the higher classes), 
that the alimentary cavity and sanguiferous canals are destitute of proper parietes, 
being simple excavations or passages in the granular pulp of the body : for in the 
Nematoneura (a name applied to the higher division of Cuvier’s Radiata by Owen), the 1 
digestive organ is provided with a proper muscular tunic, and floats in an abdominal i 
cavity : and those classes which manifest a circulating system distinct from the diges- 
tive tube possess vessels with proper parietes, distinguishable into arteries and veins. ; 
No nematoneurous class presents an example of generation by spontaneous fision or 1 
gemmation, but these modes of reproduction are common in the acrite division. Some 
of the latter, however, are oviparous ; and in a few the sexes are separate.] i 
* Before my time, modern naturalists divided all invertebrated ani- 
mals into two classes, the Insects and Worms. I was the first to attack 
this method, and presented another division,in a Memoir read before the 
Natural History Society of Paris, on the 10th of May, 1795, and printed 
in the Decade Philosophique, in which I marked the characters and 
limits of the Mollusks, Crustaceans, Insects, Worms, Echinoderms, 
and Zoophytes. I distinguished the red-blooded worms, or Annelides, 
in a memoir read before the Institute on the 3Ist of December, 1801. 
And finally, in a Memoir read before the Institute in July, 1812, and 
printed in the Annales du Mus, d’Hist. Nat., tom. xix., 1 distributed 
these various classes under three grand divisions, each of which is 
comparable to that of the vertebrate animals. 
t Synopsis Entozoorum, p. 572. 
t Lamarck observes : — “ The Apathetic Animals,” (as he terms the 
Acrita,) “ have been very improperly called Zoophytes ; as their nature 
is completely animal, and in no respect vegetable. The denomina- 
tion of Rayed Animals is also objectionable, as it applies only to a 
portion of them. — Anim. sans Fertibres, i. p. 890. 
§ Cycloptedia of Anatomy and Physiology, Art. Acrita ; from which 
the succeeding passages are also abridged.— Ed. 
li 
