90 
THE VOYAGE OF H.M.S. CHALLENGEK. 
have all passed up from the abdomen — and if the incubatory pouch is then formed in 
such a way that the ova which have been fertilized last pass in first, and so reach the far 
end of the pouch, then the observed arrangement would be brought about. But I have 
no reason to believe that this is the actual process, as no Ascidiozooids were found with 
the peribranchial cavity full of ova and embryos for the reception of which an incubatory 
pouch had not yet been formed. 
The Process of Budding . — As this account is taken from the observation of 
some chance sections of buds occurring in a few preparations of sliced stems, many 
gaps of course exist, and many points remain undetermined on account of sections in 
the proper direction, and at the proper stage of development, not being obtainable. 
Further study with more abundant material will be required to unite the various links 
and supply all details. 
It has been already seen that from the abdominal region of each Ascidiozooid in 
the colony a long appendage extends downwards towards the base of the peduncle, 
that this appendage consists of a blood sinus in direct communication with the posterior 
extremity of the heart, and of a covering derived from the mantle or body-wall, and 
that in the peduncle these appendages lie in tunnels bored through, and separated from 
each other by, the investing mass (PI. VIII. fig. 9). 
These vascular appendages, as might be expected from their nature, contain blood- 
corpuscles ; in the preserved specimens, however, the corpuscles are never very abundant. 
Throughout the greater part of an appendage they are scattered singly and sparingly ; 
here and there, however, at or below the middle of the stalk, clusters of them may be 
seen adhering to the walls of the tube. These clusters vary in size from twm or three 
corpuscles up to a dozen or so ; in the latter case it may be generally observed that the 
wall beside them bulges a little outwards, so that they occupy a slight recess (PI. IX. 
fig. 2). Probably the corpuscles now begin to di\dde, at any rate their number increases 
rapidly, so as to form a more or less spherical cellular mass placed in a diverticulum of 
the appendage. This is the beginning of the formation of a bud. This mass of cells 
increases in size and becomes ellipsoidal or almond-shaped (PI. IX. fig. 3). The cavity 
in which it lies also enlarges, works its way into the adjacent investing mass, and finally 
becomes entirely shut off from the tube of which it originally formed a part (see PI. IX. 
figs. 4, 5). 
Before this migration has taken place the cells of the bud have come to be arranged in two 
concentric layers (see PI. IX. figs. 3, 4, 6). How this takes place I was unable to 
determine. Probably the outer layer is formed from the v^all of the vascular appendage 
(which is covered by an extension of the ectoderm) and the inner by a rearrangement of 
the blood-corpuscles (usually regarded as mesoderm cells). Two layers, however, are 
produced, an outer or ectodermic and an inner or endodermic, the latter enclosing a 
cavity, the archenteron. 
