158 LEI OIM Ee [Vor. XII. 
this particular the last named species agrees about as well 
and about as little with G. coccinea as with S.zncrustans. But 
it is when we regard the branchial sacs of the two species now 
being compared that we find their most important differences. 
The sac of Syzstyela incrustans has a rudimentary fold on each 
side, while it will be remembered that no folds are present in 
G. dura. Unfortunately, Herdman does not tell us the number 
of internal longitudinal vessels in the sac of either G. coccinea 
or S.zucrustans; but he has shown eight in a figure of a por- 
tion of the sac of the latter, so we are certain that the number 
here exceeds the number in G. dura by at least three; of 
course the excess may be greater, since it is not certain that 
the eight shown in the figure referred to is the entire number 
present; in fact it is more likely not to be, since in making 
such preparations of the sacs as that from which this figure 
was drawn one does not usually obtain intact the entire width 
of one side. 
In S.zucrustans there are intermediate vessels, ‘normally 
three in number,” crossing the meshes of the branchial sac. 
In G.duva I have never seen more than one of these, and 
frequently this one is absent. 
There also appears to be a difference between the two 
species in the arrangement of the polycarps. In the former 
they are figured by Herdman as scattered promiscuously over 
a portion, at least, of the wall of the peribranchial cavity, while 
in the latter, so far as I have found them present, they are 
confined to a single row on each side of the endostyle. But 
great weight cannot be attached to this distinction, since the 
sexual organs are too poorly developed in all my specimens of 
G. dura to enable one to decide what their arrangement might 
be in a better-developed condition. 
3. THE Zooips IN THE COLONY. 
This subject is so intimately connected with that of bud- 
development that it must be treated somewhat more fully than 
have been the other points of adult structure. I cannot dis- 
cover any constant arrangement of the Ascidiozooids in the 
