374. ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
of the hemal surface ; and the buds remain, in nearly the same plane 
as that in which they were given off, until they have attained some 
distance from the parent. It has been seen, in fact, that three buds 
given off successively from one ascidiozooid, may be visible, one below 
the other, in the same, not very thick, longitudinal section. But in 
the tetrazooid, as in the adult, the hemal side is that turned away 
from the aperture of the ascidiarium. If, then, the buds thrown off 
from the ascidiozooids of the foetus all remain on the hemal, or apical, 
side of their parents, we ought, on examining the adult organism, 
to find the four primitive ascidiozooids close to the margin, with a 
series of two or three buds, in various stages of development, 
attached to each. 
As a matter of fact, however, no section taken near the margin of 
the aperture has ever presented an appearance essentially different 
from that represented in Pl. XXX. [Plate 29] fig. 4. The ascidio- 
zooids have always been young, and, on the average, younger, the 
nearer they were to the margin. But they have never been younger 
than such a bud as is represented in fig. 24, Pl. XXX. [Plate 29]; 
and those of the first three or four tiers have always possessed 
imperfectly developed sexual organs, and buds not more advanced 
than those represented in figs. 19 and 20. 
That the ascidiozooids which lie nearest the aperture are the re- 
sult of the budding of other ascidiozooids is beyond all doubt. As I 
have traced the development of the stolon from such a modified bud, 
it is clear that the bud is not developed, as I had once imagined, 
from the stolon of another ascidiozooid,—these stolons being in- 
variably traceable, without a break, into the lip of the cloaca, where 
they end cecally. There appears to me, then, to be no other course 
open but to suppose that these young ascidiozooids which lie nearest 
the aperture, are buds which were originally developed from the 
hzmal region of ascidiozooids which lie nearer the apex, and that 
they have consequently passed round and to the neural side of their 
parents. If this migration of the buds really occurs, it will follow, as 
Savigny supposed, that the four apical ascidiozooids of the adult are 
the modified zooids of the fcetus,—the buds developed from their 
haemal walls not remaining upon their apical side, but passing up 
between them on to their neural sides, and there becoming them- 
selves new centres, whence fresh buds are thrown off, which gradually 
take their places in a still higher tier. 
I can conceive of no other mode in which the structure of the 
foetus, the structure of the adult and the law of budding can be 
reconciled ; and yet I am reluctant to admit so seemingly artificial a 
