XX INTRODUCTION. 



That the function of Respiration should be widely dif- 

 fused and very simple in these animals will follow from 

 what has been said. The chylaqueous fluid, consisting 

 largely of sea-water admitted freely from without, is itself 

 a reservoir of oxygen, and thus its organized elements are 

 perpetually aerated. We have already seen how the ciliary 

 currents within maintain a constant succession of the 

 bathing fluid upon every part ; and there can be no doubt 

 that some mode of exit is provided for the effete water. 

 What this is, however, I know not. In Cerianthus, which 

 has a posterior foramen to the body-cavity, I have seen the 

 water forcibly ejected from this aperture (see infra, p. 272) ; 

 I have also marked a sudden jet d'eau from the disk (pro- 

 bably from the mouth, but of this I was not sure) $ of 

 T. crassicorm's, which shot up some mucous shreds with 

 force to the surface, a height of some five inches. Perhaps 

 these expulsions, and those from the tentacle-tips already 

 alluded to, may be set down as so many expirations (per- 

 haps periodical) of deoxygenated water. 



Ancillary to respiration, as renewing the water in the 

 vicinity of the animal, is the ciliation of the external sur- 

 face. This is strong and uniform on the tentacles, but 

 I have never been able satisfactorily to trace it on the 

 column. It is first visible at the margin, flowing in an even 

 current up the tentacle, on every side, from the foot to the 



I saw with a lens, for an hour together, with the utmost distinctness, a 

 small circular (oval in perspective) foramen in each septum. That is, I saw 

 them in a dozen or more successive septa, without interruption. The 

 diameter of the foramen was about the same as that of a tentacle near the 

 tip, in its ordinary state of extension. That the foramina were in films 

 whose surfaces were coincident with the line of vision, and not transverse 

 to it, I proved, by moving my eye to the right and left, by which the 

 foramen became more and more round, or more and more linear, the line 

 in the latter case being that of the axis of the column. Hence they must 

 have been in films running from the column-wall towards the axis perpen- 

 dicularly, as regards the position of the animal; — conditions which agree 

 with the septa, and with them only. 



The next day, with a very favourable sight, I traced the foramina conse- 

 cutively for half the circumference of the animal. In this space there 

 were 49 septa (perhaps one more than the half, for I bisected only with nry 

 eye) ; and I found that the foramina are pierced through those which are 

 entire (by far the greater number), but that the series is interrupted irre- 

 gularly by those imperfect septa, which span the cavity like an arch The 

 latter were invariably two together, differing much in the height of 

 the arch, and graduated in this respect. The detail of the numbers of the 

 consecutive septa, in the half-animal, stands thus : — 



Perforate— 13 . 2 . 10 . 4 . 2 . 2 . 2 . 

 Imperforate— . 2.2 . 2.2.2.2.2 



