marked out into five short segments. One of the two terminal 
segments becomes much enlarged, spreading over and investing one 
pole of the ovisac like a cup; while the other four remain far smaller, 
and, the indentations between them deepening, they are eventually 
connected only by narrow isthmuses of blastoderm. These segments 
are the rudiments of as many zooids; but the large cup-like one has 
a totally different fate from the rest, and for distinction’s sake I shall 
term it the cyathoszootd, while the others are, in their order of nearness 
to it, the Ist, 2nd, 3rd, and 4th ascidiozooids! respectively. The 
zooids are not merely connected with one another by the isthmuses 
of blastoderm above-mentioned, but the structureless test has greatly 
increased in thickness, and now invests them all, like a thick layer of 
transparent varnish. The membrana propria of the ovisac is no 
longer distinguishable outside this rudimentary test. 
The remains of the duct are often still traceable, towards the con- 
clusion of this stage, at one end of an equatorial diameter of the 
fcetus (supposing the cyathozooid to be situated at one of its poles) ; 
but later, it is no longer to be discovered. 
Eighth Stage. Fatuses from psth of an inch up to the largest which 
have been met with, 
In describing this final stage of development, it will be convenient 
to consider, first, the changes in general arrangement, size and form, 
of the different parts of the foetus; and secondly, the special modifi- 
cations which each of these parts undergoes, 
The cyathozooid, at first, occupies but a comparatively small seg- 
ment of the surface of the spheroidal fcetus, and the slightly curved 
series of ascidiozooids stretches out from it, over about half the circum- 
ference of the uncovered portion of the ovisac (Pl. XX XI. [Plate 30] 
fig. 11). But, by degrees, the cyathozooid extends so far as to invest 
nearly half the surface of the ovisac, and, at the same time, the 
chain of ascidiozooids (considered as a whole) gradually assumes a 
new direction, and applies itself closely to the face of the cyathozooid, 
whose circumference it half encircles (fig. 13). The blastoderm of 
the ascidiozooids, however, remains perfectly distinct from that of the 
cyathozooid, the two being united only by the layer of test, which, in 
the earlier stages, invested both, and whose contiguous edges now 
seem to run into one another. 
I have, throughout the present memoir, used the term ‘ascidiozooid,’ as more 
-euphonious than ‘ascidiite,’ employed in my notice in the ‘Annals of Natural History’ for 
1860. 
