220 
MR. J. S. BOWERBANK ON THE ORGANIC TISSUES IN THE 
of the observer the idea, that this mode of disposition could have obtained only in 
consequence of their having been originated within the parietes of vascular tissue 
(Plate XVII. fig. 1). At the same time I must state, that I have examined many such 
branching series of these organs without being able to detect any remains of the sup- 
posed vascular tissue, which it is possible may have been absorbed after having per- 
formed the office for which it was produced ; and this view of their origin is the more 
probable, as we observe, in many cases, the minute vascular tissue, so abundantly 
dispersed amid the whole of the membranous structure, frequently filled either with 
continuous threads of a glutinous looking matter, or of an abundance of minute de- 
tached molecules, and in one instance, represented in Plate XVII. fig. 2, 1 observed a 
series of molecules, with a few minute cytoblasts intermixed, continued beyond an 
irregular and indistinct termination of a vessel, no part of the parietes of which 
could be detected around any portion of the line of molecules and cytoblasts. 
Whatever may be the origin of the cytoblasts, it is sufficiently apparent that their 
office is that of the production and renovation of the cellular membranous structures 
of the bodies in which they appear. 
Upon examining the animal matter obtained from Agaricia ampliata, I found them 
developing cellular tissue upon all parts of the membrane, spreading thinly over the 
surface of the tissue, and, when several of them were situated together, assuming the 
appearance of a rude reticulated epidermal tissue. 
One of the most interesting of their modes of developing tissue was seen upon ex- 
amining the animal matter obtained from Cellepora pumicosa. The membranous 
tissue is exceedingly thin and even in its structure, beautifully diaphanous, and 
abounds in large sacculated projections (as represented in Plate XVII. fig. 3). At the 
termination of each of these we observe a cytoblast, which is attached to the surround- 
ing membrane by the outer circle of its disc, from all parts of which it has projected 
the thin filmy tissue in a backward direction, thus producing the elongated sacculated 
organ upon the summit of which it is seated, and causing its apex frequently to as- 
sume a truncated or flattened appearance. The sacs may be seen in every degree of 
development from the cytoblast, scarcely elevated above the surface of the membrane, 
until they are projected to the extent of eight or ten times the amount of their own 
diameter. The projection of the sac is usually in the direction of a straight or slightly 
curved line; occasionally it forms an abrupt elbow; but in all cases the cytoblast 
retains its place at the extremity of the organ. Sometimes, but very rarely, there 
are two cytoblasts at the apex, which, having operated simultaneously, cause the organ 
to assume an oval instead of a cylindrical form. When the apices of two of these 
sacs meet, as represented at a, Plate XVII. fig. 3, they coalesce and appear to form 
a permanent union, but I have not observed that this takes place when they impinge 
upon any other part of the sac. 
As the sac elongates, we frequently find it accompanied by minute vessels, which 
usually but not universally, assume a spiral direction, as seen at b, Plate XVII. fig. 3, 
