348 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
becoming metamorphosed into the vas deferens, while the broad end 
increases in size, and is directed more forwards as well as upwards. 
In a bud +-th of an inch long (fig. 24) the testis measures ;3,5th 
of an inch in length, while its broad end is above -1,th of an inch 
thick. The apex of the vas deferens already pushes a little eminence 
of the atrial tunic before it. 
In a young ascidiozooid, somewhat more advanced than that 
represented in fig. 25, the’vas deferens is ;3,th of an inch in length, 
and is of nearly even diameter throughout, except at its upper end, 
where it is slightly dilated and plainly hollow. It is connected with 
the posterior part of the terminal enlargement, which is nearly 35th 
of an inch thick, and is divided into three short lobes, each about 
sooth of an inch thick. Like the previously existing pyriform 
enlargement, these rudimentary czca are solid masses of indifferent 
tissue. Traces of a distinct membrana propria are discernible around 
each cecum. In still larger ascidiozooids the number of caca in- 
creases, and the whole organ becomes larger, until it assumes its adult 
form ; and it is only when nearly in this condition, that spermatozoa 
are visible in the vas deferens and the adjacent parts of the ceca. 
The development of the ovisac will be described below. At first 
both the testis and the ovisac have ample room within the sinus of 
the zooid in which they are lodged; but as they increase in size, the 
duct of the ovisac extending towards the neural side and forwards, 
and the duct of the testis extending towards the neural side and 
backwards, push the atrial tunic before them, so that their openings. 
are eventually situated on slight papillary elevations. The principal 
portions of the two organs, on the other hand, consisting of the sac of 
the ovisac and the ceca of the testis, as they enlarge, pass into 
chambers in the test, which are formed for them by the recession of 
the outer tunic, and whose cavities, consequently, communicate freely 
with the hamal blood-sinuses. 
With respect to that part of the generative blastema which remains. 
in connexion with the endostylic cone, one of its endoplasts or nuclei 
soon acquires a larger size, and becomes surrounded by a clear space,. 
thus giving rise to a new germinal vesicle and spot, round which will 
eventually be formed the solitary ovum and ovisac of a new bud, 
developed from the zooid, whose origin has just been traced, in 
exactly the same way as itself has arisen. 
Thus, if we start with a single ascidiozooid, it may give rise, to all 
appearance, to an indefinite succession of buds, by successive enlarge- 
ments and detachments of the end of the peduncle of the first ; 
and each bud thus developed carries within itself, in its generative 
