85 
*' n< l that the external characters of the Radiala are engrafted 
an a type of tunicated Mollusca : characters, though distinct 
rn m each, which yet soften away into both. Some of the 
Slypes of this order have been arranged by most authors 
a, »ong the Hy droid as, in consequence of their polypidoms 
t< “sembling those of the Sertulariadse. By the examination 
^ tlieir polypes, however, they are now transfered to the 
polluscan zoophytes; and this grouping seems far from 
cing unnatural, even when their external forms are con- 
8 ><lercd. Whatever alteration may be made in the future 
^fangoment of these creatures, when they shall have been 
•ttore thoroughly studied, vet the making the polype the 
r °'iudation on which to rest, is the only true one to guide 
*"<! systematist. The order is characterized as “ Polypes 
a 99 r egate, the mouth encircled with filiform , ciliated, re- 
(, «c tile tentacula ; stomach distinct, with a curved intestine 
^‘titillating in an anus near the mouth ; ova internal. Poly- 
Jndojjjs very variable j either horny, fistular, and confervoid, or 
n>e »ibranous or fi bro-gelatinous ; formed of cells connected and 
Ranged in a determinate, and usually quincuncial manner .” 
As the polype, therefore, forms the foundation of the ar- 
^tgement, it will be necessary to describe it, though without 
6r deiing into minute detail. In its expanded state it stands 
•’•‘eminently from the cell; it is columnar and transparent, 
!° that the internal structure can be seen. Between the sur- 
. of the polype and the internal organs, there is an 
'' lte rvening space, similar to what has been noticed in the 
. Ceroid zoophytes. This space is said to be occupied by 
a dear fluid; and here also are the muscles, by which tbo 
Mype effects its various and rapid motions. 1 be upper 
i tiou of the column is surrounded with numerous long 
® e nd er tentacula. In the foregoing orders it lias been found 
*"’ u the chief uses of the tentacula were lor the capture of 
■ e y; here their functions have undergone a complete revo- 
j J ; here lueir luneuous u<ive ~ - 
j U °i>, for to them belongs the function of respiration, and 
J 1 a secondary degree only that of nutrition. If an expan- 
. ° c ' polype be examined with a microscope, it will be found 
fesemble a minute and delicate flower endowed with son- 
a hou aij( j voluntary motion. The tentacula which are long 
slender, arc cloalhed with numerous minute cilia, which 
! re in a constant slate of activity. By their vibrations 
* l >Uierous currents pass over the tentacula and across the 
.,* a i surf acei Any insect or other substance coming within 
j‘ le ? e currents, passes over the mouth, and in so doing it 
c ,n stantly caught by the prehensile lips, wliich arc ex- 
^cuingiy sensitive, and conveyed to tiio stomach. Thus 
i,° s ee Loth oilices are performed by one set ol organs, one 
