42 
STRUCTURE AND PHYSIOLOGY 
is very similar to what has been observed in the Charaand other 
plants, in the Sertularia ; and recently Mr Lister has confirm- 
ed this discovery, and ascertained the existence of the same 
phenomenon in almost all the genera of the order. The result 
of his curious observations is thus summed up by Dr Rogefc. 
<c In a specimen of the Tubularia indivisa, when magnified one 
hundred times, a current of particles was seen within the tubular 
stem of the polype, strikingly resembling, in the steadiness and 
continuity of its stream, the vegetable circulation in the Chara. 
Its general course was parallel to the slightly spiral lines of ir- 
regular spots on the surface of the tube, ascending on the one 
side, and descending on the other ; each of the opposite cur- 
rents occupying one-half of the circumference of the cylindric 
cavity. At the knots, or contracted parts of the tube, slight 
eddies were noticed in the currents ; and at each end of the 
tube the particles were seen to turn round, and pass over to the 
other side. In various species of Sertulariae, the stream does 
not flow in the same constant direction ; but, after a time, its 
velocity is retarded, and it then either stops, or exhibits irregu- 
lar eddies, previous to its return in an opposite course ; and so 
on alternately, like the ebb and flow of the tide. If the cur- 
rents be designedly obstructed in any part of the stem, those 
in the branches go on without interruption, and independently 
of the rest. The most remarkable circumstance attending 
these streams of fluid is, that they appear to traverse the cavity 
of the stomach itself, flowing from the axis of the stem into that 
organ, and returning into the stem, without any visible cause de- 
termining these movements.” * 
The power which sets in motion and maintains this current 
is yet undiscovered. Professor Grant asserts that it depends 
on the action of minute vibratile cilia, — 66 the common agents 
of all analogous movements in the lowest tribe of animals, ’’f — 
but no direct observation has confirmed this explanation, which, 
it will be observed, is founded on analogy only, and it has this 
in opposition — that the non-existence of cilia in the external or- 
gans of the zoophytes in question has been distinctly proved. 
* Bridgew. Treat. Vol. ii. p. 233. See also Tiedemann’s Comp. Physiol, 
p. 150, Ent. Mag. Vol. iii. p. 174 : and Grant’s Outlines of Comp. Anat. p. 
429-30. 
f Outlines of Comp. Anat. p. 430. 
