344 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
coalesced, but that it is, originally, a simple imperforate dilatation of 
the pharyngeal portion of the alimentary canal. The development of 
the atrium adds a second or outer wall to this dilatation; and when, 
by the formation of this double wall, the branchial sac is constituted, 
the stigmata make their appearance in its parietes—the atrial and the 
pharyngeal walls becoming united around the margins of each 
stigma. 
When a bud has attained a length of between j-th and 4th of an 
inch, the narrow neck connecting it with the peduncle is obliterated, 
and it lies free in the general test of the parent ascidiarium. It next 
elongates until its oral and atrial apertures are placed in connexion 
with the exterior and the cloaca respectively (the latter connexion 
appearing to be effected first), and then it increases in depth until it 
acquires the appearance of the adult. Before it is detached, however, 
the portion of the peduncle nearest it enlarges and assumes the shape 
of a new bud; so that the proximal end of the peduncle now passes. 
into a small bud with whose apex a larger one is connected (fig. 22). 
And I suspect that this process is repeated as long as there is any 
reserve of generative blastema in the parental organism. I have, 
however, never actually seen more than two buds thus connected 
together. As the buds are all developed from the hemal region of 
the pre-existing ascidiozooids, it follows that the new ascidiozooids. 
formed by gemmation must at first be thrust among the old ones, 
towards the apical end of the ascidiarium. 
So much in elucidation of the mode in which the buds attain the 
form and general arrangement of organs characteristic of the adult. 
I now proceed to speak of such among the minor changes which 
these organs undergo as call for particular remark. 
Of the outer tunic all that requires to be said is, that it becomes 
relatively thinner as development goes on. In buds which are situated 
within acertain distance of the open end of the ascidiarium, and which 
-haveé attained a length of ;,th of an inch (fig. 24), the outer tunic of 
the neural wall of the atrium is raised into a slight rounded projection 
(72), and in older buds (fig. 25) this gradually elongates, and extending 
towards the open end of the ascidiarium, and finally into the lip of 
the cloacal aperture, becomes converted into one of the stolons of the 
test. 
The atrial muscular bands are visible in buds not more than {jth 
of an inch in length (fig. 23); the pharyngeal muscular bands, only in 
more advanced zooids. 
The tentacular fringe appears first as an inward thickening of the 
parietes of the mouth. The hemal tentacle is markedly the longer, 
