VOL. I1.] , Balanogtossus. 199 
raised a doubt that all belong to one genus—which is the 
more primitive way of development, directly without the larval 
stage, or through the larva? Did the first Balanoglossus reach its 
developmental goal by the long, indirect tornaria road, and did a more 
modern one, imbued with the rapid transit idea, cut across lots leav- 
ing the ancient roundabout way? Or did the older forms go across 
while the younger ones have taken to the longer road? No one 
has discussed this question at any length, andI am not going to un- 
dertake it at present. In fact without a knowledge of the first stages. 
of development of the Tornaria, it would probably be impossible to 
arrive at any very satisfactory conclusion on the subject. It is sug- _ 
gested by Korschelt & Heider” that the direct development is 
the more primitive, their reason for this conclusion being found 
in the fact that the mouth and anus do not form in this larva till a 
comparatively late stage—a condition which would seem to be in- 
compatible with a free swimming of larva. 
There are, however, some quite serious difficulties in the way of 
this suggestion, one of which is that the circumanal ciliated band 
appears very early in the directly developing species, while it forms 
quite late in the Tornaria. : 
For the solution of this question, as well as of several others, it 
is of the utmost importance that we fill up the gap that now exists 
in our knowledge of the earliest embryonic stages of Tornaria; and 
to this end the more species we have access to, the better become 
our chances of being able to do this. It is quite probable that 
somewhere on our great extent of sand and mud beach a represen- 
tative of the genus will be found. 
' EXPLANATION OF THE FIGURES OF PLATE XXII. 
Fig. 1. Balanoglossus kowalevskii. (After A. Agassiz, from Korschelt 
and Heider.) 
Fig. 2. Sagittal longitudinal section through the proboscis and collar of 
Balanoglossus sarniensis. (After Kéhler, from Korschelt and Heider.) 
Fig. 3. The young Balanoglossus, shortly after its transformation; under 
the compressor. 
Fig. 4. The anterior portions of a Tornaria shortly before its transforma- 
tion to Balanoglossus. The larva was flattened down somewhat by the com- 
pressor. The outlines drawn with a camera lucida. 
Fig. 5. A Tornaria at a somewhat older stage than Fig. 6, to show internal — 
structures. 
NESE. 
