504 
HUBERT LYMAN CLARK 
are no traces of radial water vessels and the development of the 
water-vascular, nervous, sensory, muscular and alimentary sys- 
tems is, so far as I can see, identical in the two genera. In Synap- 
tula the mouth is formed much earlier and the atrium develops 
on the ventral side instead of at the anterior end, but these dif- 
ferences cannot be regarded as of any particular importance. They 
are doubtless due to the accelerated development of Synaptula. 
The living pentactula of Chiridota is most interesting to watch, 
for the tentacles, which serve as sensory, locomotor and feeding 
organs, are in constant motion, while the surrounding collar seems 
to be equally active. Possibly its movements may be respiratory, 
but I am rather inclined to think they are merely the result of the 
activity of the tentacles. In the older pentactulas, the tentacles 
are vertically notched at the tip ; the depth of this notch increases 
with the growth of the tentacle, and thus the pair of terminal 
digits is formed. 
None of the Chiridotas collected in Jamaica contained young 
beyond the pentactula stage, but several Bermudan specimens 
provided older material. The principal changes which occur in 
the course of growth are the complete disappearance of the ciliated 
bands and the atrial collar, the marked development of the two 
terminal digits on the tentacles, and the appearance of groups of 
the characteristic six-spoked wheels. The calcareous ring is more 
noticeable and calcareous rods appear in the tentacles. Neither 
at this stage, nor in the pentactula, are there any glandular 
organs" or ''contractile rosettes" present in the skin, such as are 
found in Synaptula hydriformis and Leptosynapta minuta. At 
the close of the pentactula stage, the secondary outgrowths of the 
hydrocoel, which have remained quiescent beneath the radial 
nerves, begin to show signs of activity. Their subsequent devel- 
opment is exactly as in Synaptula, except that the}^ do not grow 
simultaneously. The first to develop are those under the latero- 
ventral nerves ; these push out dorsal to the nerves and thus give 
rise at the same tim.e to the sixth and seventh tentacles. This 
seven-tentacled larva (fig. 6) was first observed by Ludwig ('81) 
in Chiridota rotifera, and subsequently ('98) by the same eminent 
zoologist in Taeniogyrus contortus. It appears to be a well- 
