; ACTION OF BLOOD-VESSELS IN NUTRITION. . 323 
fluid into the neighbourhood of the part where it is to be 
employed ; and the blood, orat least its organizable portion— 
the liquor sanguinis—must quit the vessels before it can be 
in the development of new tissue. We might illus- 
‘strate this by the distribution of water-pipes through a city ; 
they might pass into every house, nay, into every room, and 
yet the water must be drawn from the pipes before it can be 
applied to any required purpose. The spaces untraversed by 
‘vessels have been shown to be larger in some tissues, and 
‘smaller in others; the distribution of the capillaries being 
‘more minute, in proportion as the nutritive actions of the 
‘part go on more energetically. Now in the embryo, even of 
the most complex and perfect animals, there is a period when 
no blood-vessels exist, the whole mass being made-up of cells, 
every one of which lives for itself and by itself, absorbing 
nutriment from a common source, and not at all dependent 
pon its brethren. It is only when a diversity of structure 
begins to show itself—one part undergoing transformation 
into bone, another into muscle, and so on,—and when some 
portions of the fabric are cut-off from the direct supply of 
nourishment,—that vessels begin to show themselves. These 
re formed, like the ducts of Plants, by the breaking-down of 
the partitions between contiguous cells; they at first seem 
tather like passages or channels, than tubes with walls of their 
; and this condition they retain in certain cases through 
ife (§ 289). 
Repair of Injuries. 
_ 389. Every animal possesses, in a greater or less degree, 
the power of not merely maintaining its organized fabric in 
ts integrity, by the renewal of the parts which are from time 
to time ing into decay, but also of reproducing parts of 
that fabric which have been lost by disease or accident. This 
power seems greatest among the lowest tribes of Animals ; in 
many of which the entire organism can be reproduced from a 
all portion of it, as is the case with the Hydra (§ 122), and 
vith some species of Sea-Anemone (§ 126). In the Star-fsh, 
t far more highly-organized animal, the regenerative power is 
More limited, though it is still very remarkably manifested ; 
or if one, two, or more of the rays be broken or cut off, they 
e gradually restored, pores the central disc be uninjured. 
Y 
