No.1.] THE DEVELOPMENT OF BALANOGLOSSUS. 65 
Metamerism of Balanoglossus. 
To those who accept the chordate affinities of Balanoglossus 
the question of metamerism of the Enteropneusta is full of 
interest. But even leaving the phylogenetic question out of 
account, the problem is of importance in itself. Our ideas 
as to metamerism have been largely based on the typical meta- 
meric structure of Annelids and Vertebrates. And, more or 
less closely bound up with our conception of metamerism in 
these groups, the budding theory has played no small part. 
It is true that other views have been advanced regarding meta- 
meric structures as due to the mechanical motions of the body. 
To state the two opposing theories briefly, if somewhat crudely, 
the former starts with a short animal and elongates it by serial 
repetition of itself (budding), while the latter, taking an elon- 
gated animal, breaks it up into a series of smaller but similar 
subdivisions. 
For myself, I think a much broader view must be taken of 
the subject, but the time is not yet ripe for new theories, 
and what we need most is more facts. It is not my intention, 
therefore, to go any further into the subject at present, and 
what I have already said is to prevent misconstruction of what 
I shall say in regard to Balanoglossus. 
I regard Balanoglossus as a form having three pairs of body- 
cavities, each pair separated in the dorsal and ventral lines by 
longitudinal mesenteries, supporting (at least for the second 
and third pairs) the intestine. 
The pairs of body-cavities are separated from one another 
by transverse septa, with double walls. This is more apparent 
for the transverse septa between the collar-cavities and the 
last pair than between the collar-cavities and the first pair. 
Now, in both of these respects the structure of Balano- 
glossus agrees with two very important features of Annelids 
and Vertebrates. Even the external divisions of the body 
correspond with the internal divisions into metameres, and 
of course the muscle-system agrees with the same arrange- 
ment. Now, I fancy if Balanoglossus were shortened, —the 
proboscis changed into a pre-oral lobe and the posterior 
