26 MORGAN. [Vou. IX. 
contact with the endodermal walls and in the same position as 
in the New England Tornarta. 
In this respect the Bimini form differs greatly from the 
Bahama Tornaria, and while it shows an approximation to the 
latter form in the development of tentacles, it stands nearer to 
the New England type in the position of its second and third 
pairs of body-cavities. 
The anterior body-cavity is present in the larva. It is con- 
nected with the apical plate by a long process from its wall. It 
opens to the exterior to the left of the middle line by a single 
exit tube. 
To what species of Balanoglossus this Tornaria gives rise I 
do not know. 
INTERNAL (AND MICROSCOPIC) STRUCTURES. 
Serial sections of larvae of Stage 1, Pl. I, show that at 
this early stage the body-wall is both relatively and absolutely 
thicker than in the later stages. The cells are not so much 
flattened as. in ‘the later’ (stages, ~Fig. 1, PE TIT ‘shows: a 
cross-section of the body-wall in the middle lateral region. 
At one point in the section is found a large, oval, clear spot, 
with a nucleus at each side; this corresponds to one of the 
large black dots seen on the surface of the living larva, but its 
pigment has been dissolved out by alcohol. The extra-oral 
ectoderm is at this level thinner than the circum-oral. One of 
the tentacles, cut in longitudinal section (in the cross-section of 
the body), is shown in Fig. 2. The section cuts the length 
of the ciliated band of the tentacle. The nuclei are found 
several layers in depth, and are smaller than those of the rest 
of the body-wall. The blastocoel cavity is continuous into 
the cavity of the tentacle. The cilia of the band were prob- 
ably eaten off by the hardening fluid. The circular ciliated 
band is found to be composed of several rows of large cells 
fitting over one another like the shingles on a roof. 
The blastocoel cavity lying between the ectodermal body- 
wall and the digestive tract is filled with a jelly-like fluid, 
and through this are found mesenchyme cells with radiating 
pseudopodia, A dozen such cells may be found in a single 
