DEVELOPMENT OF AX APODOUS HOLOTHURIAN 503 
rectly identified. These auricularias were not raised from the eggs 
nor was their development carried beyond the pentactula stage; 
they were collected in the tow at Naples and no evidence is offered 
to show that they are really the young of Labidoplax. It is true 
that no Chiridota is known from the Mediterranean Sea, but 
Semon himself discovered at Naples the interesting Trochodota 
venusta, which has wheel-shaped deposits like those of Chiridota. 
I venture to suggest, therefore, that the question as to what auric- 
ularia Semon studied is still open, and until further evidence is 
offered, I must decline to believe that young synaptids ever de- 
v^elop wheel-shaped deposits. This position is strengthened by 
the fact that in Synaptula hydriformis the first calcareous parti- 
cles to appear are simple, straight rods, from which (except in the 
tentacles of course) the plates and anchors rapidly develop. 
Pentactula larvae of Chiridota were found in many adults, 
both at Port Antonio and in the Bermudan material, and one of 
them is shown in fig. 4. No young were found between the stage 
shown in fig. 3 and the fulh' developed pentactula, but it is not 
difficult, in the light of what we know about the development of 
Synaptula, to see how the greater complexity has been brought 
about. The most important changes are at the anterior end, 
where an invagination has apparently taken place, giving rise to 
an atrium, in the center of the floor of which the mouth has arisen 
by further invagination. The growth of the tentacles upward 
around the mouth leaves the wall of the atrium, for a time, as a 
conspicuous collar surrounding the five tentacles. The latter are 
square-tipped and provided with a greatly thickened glandular 
and sensory epithelium at their free ends, particularly on the outer 
side. The alimentary canal has pushed backward to the extreme 
end of the body, where the permanent anus has formed. The 
''anterior coelom" on the pore-canal is scarcely visible, but the 
polian vessel, positional organs and radial nerves are all conspicu- 
ous. The beginnings of the calcareous ring are also plainly visible. 
Traces of the ciliated bands may still be seen on the body. Except 
for these, the atrial collar, the shape of the tip of the tentacles, and 
the wheel-shaped deposits in the body-wall, the pentactula of 
Chiridota agrees in all particulars with that of Synaptula. There 
