No.1.] THE DEVELOPMENT OF BALANOGLOSSUS. Fit 
To summarize: /z the New England Tornaria, the origin of 
the proboscis body-cavity 1s unknown. The collar-cavities arise 
each from a single proliferation of endodermal cells, and the 
third patr of body-cavities arises as solid evaginations from the 
endoderm. 
In the Bahama form described in the present paper, the 
origin of the first pair of body-cavities was not found. The 
proboscis vesicle seems to arise from mesenchyme cells. 
The collar-cavities differ fundamentally as to their origin 
from the methods followed in other forms; they arise at 
points far distant from the endodermal tube of the digestive 
tract, and come from cells resembling in every particular the 
scattered cells of the blastocoel space. Moreover, they do not 
arise from a single cell or group of cells, but from many such. 
These subsequently run together into a single body-cavity on 
each side of the body. Similarly, the third pair of body- 
cavities has a mesenchymatous origin from many separate 
cells of the blastocoel. 
To summarize: The origin of the first pair of body-cavities 
in the Bahama Tornaria ts unknown. The collar-cavities and 
the last pair of cavities have a mesenchymatous origin, and 
come from many scattered cells united secondarily. 
In drawing our conclusion, we are obliged to leave out of 
account the proboscis body-cavity, owing to absence of data 
for comparison. If we are to regard the proboscis vesicle as 
a body-cavity to be paired with the proboscis-cavity, we may 
conclude that it has in all cases a mesenchymatous origin 
(throwing out Spengel’s observation). 
The conclusion reached in respect to the remaining body- 
cavities is an interesting one. They may arise as enteric 
atverticula, as endodermal proliferations, or even arise from 
mesenchymatous beginnings. 
The sharp lines drawn by speculative morphologists as to 
enterocoels, schizocoels, blastocoels are fading out as the evi- 
dence comes in. Phylogenetic speculations of far-reaching 
and of supposed fundamental import, based on the origins of 
mesoderm in different groups, are losing their hold as facts 
accumulate. 
