No.1.] ZHE DEVELOPMENT OF BALANOGLOSSUS. 69 
Comparisons with Other Forms. 
Although short descriptions have been given of several other 
Tornaria, only in two cases has a sufficiently detailed study 
been made that is of use to us for our present purpose. 
Metschnikoff ('69) studied in surface views the transformations 
of the Tornaria of the Mediterranean, and although his account 
is accurate as far as it goes, he was limited to a study of the 
external transformation alone. A brief note by Haldeman, 
in the circular of the Johns Hopkins University (86), calls 
attention to the similarity of the Beaufort Tornaria to the 
Mediterranean form. Bourne described (89) the Tornaria 
found on the English coast, but this seems to be, from the 
description, identical with the New England Tornaria, described 
first by Agassiz, and later by myself. 
The two forms studied in greater detail are the young of 
Balanoglossus Kowalevskii of the Chesapeake, described by 
Bateson, and the New England form, studied by Agassiz and 
myself. During the past summer of 1892 I was fortunate 
enough to clear up definitely the relationship of the northern 
and southern Balanoglossus Kowalevskii in respect to the 
development of the young. In both cases a direct develop- 
ment takes place, and the description given by Bateson for 
the young of Balanoglossus Kowalevskii of the Chesapeake will 
apply equally to the New England form (as found at Wood’s 
Holl and at Newport). The adult of the New England and 
English Tornaria is unknown, although young larvae have 
been found in both waters. 
It is not my purpose to enter into a long and minute com- 
parison of the form described in the present paper with the 
two forms mentioned above — one with a direct development, 
and the other an indirect by means of the Tornaria. Nor 
would it be profitable at present to push phylogenetic specu- 
lations beyond the limits already reached. I wish, therefore, 
to confine what I have to say under this head to a comparison 
between the formation of the body-cavities in the three forms. 
Bateson described the proboscis body-cavity as arising from 
the anterior end of the archenteron. It is cut off from the 
