316 ASAJIRO OKA AND ARTHUR WILLEY. 
and organs on the other. It is, however, necessary not to 
push this analogy too far. 
It may have been noticed that so far we have not applied 
the term “ common cloacal apertures” to the excurrent orifices, 
and we have intentionally abstained from doing so. In the 
Botryllide and Polyclinide, as has been long ago pointed out 
by Savigny, the cloacal apertures of the individuals belonging 
to a system which may be more or less regular, conspire 
together, sometimes in a very close manner, as in Botryllus or 
Circinalium, in other cases less closely, to form a true common 
cloacal aperture, which is capable of being opened and closed 
by muscular action. 
In the Didemnide as a whole, and par excellence in our 
new Didemnid, this association of cloacal apertures does not 
occur. Here the cloacal apertures of the individual Ascidio- 
zooids are perfectly distinct, and each opens independently 
into the canal-system in the way above described (see fig. 3). 
Thus, while in the Botryllide, for example, the excurrent 
orifices are true common cloacal apertures, in the Didemnidz 
they are distinctly not the same thing in the same sense, 
although they are possibly homologous structures. 
This is why we have preferred to use the term “ excurrent 
orifices.” 
8. Ascidiozooids. 
As already indicated, the Ascidiozooids cannot be seen from 
the outside in a living colony; but in preserved specimens 
they appear as very numerous white specks, which are studded 
evenly all over the colony without any reference to a system 
or systems of distribution. In fig. 2 the black points imme- 
diately beneath the surface represent the Ascidiozooids, while 
the round bodies which lie deeper in the test are the larve. 
On the structure of the individual Ascidiozooids we have 
nothing special to say, since they conform very closely to the 
Didemnid type. The most characteristic feature of all for 
the Ascidiozooids of the Didemnide is the single unpaired 
testis, round which the vas deferens is wound spirally. 
