DEVELOPMENT OF AN APODOUS HOLOTHURIAN 
511 
priman^ tentacles and the complete degeneration of the radial 
canals in the adult, in addition to the entire loss of pedicels, 
seems to me to confirm this view. In 1898, I pointed out that 
there were three possible views regarding the relationship of the 
synaptids to the other holothurians: (1) that the synaptids are 
the primitive stock of the class; (2) that the synaptids represent 
a more primitive branch of echinodernis than that of the pedate 
holothurians; (3) that the synaptids are degenerate pedate holo- 
thurians. At that time I held to the third view. The works of 
Becher and Edwards, taken in connection with my study of 
Chiridota, lead me to believe now that the second view, which 
was first proposed by C'uenot ('91), is quite as near the truth. 
While I do not think it can be questioned that the synaptids are 
degenerate, pedate holothurians, I am satisfied that the pedate 
form from which they arose (the ''Urholothurie" of Ludwig, 
'SStammholothurie" of Ostergren) differed in certain very impor- 
tant points from any known form. I picture it as a short, thick- 
bodied creature with five stout, simple, interradial tentacles, 
much like a pentactula in form and moving like it, chiefly by means 
of the tentacles. Unlike the pentactula, however, it had well- 
developed radial water-canals with each of which was associated 
a double series of pedicels. From such an ancestor the Paractino- 
poda have arisen, losing the pedicels and radial canals, while 
the Actinopoda have developed with the loss (or extraordinary 
shifting) of the five priuaary tentacles. Before the separation of 
the two sub-classes certain pedicels close to the circular water- 
canal became modified into tentacles, and in the Actinopoda, five 
of these (one in each interradius) seem to have replaced the pri- 
mary tentacles. If Edwards' and Ludwig's observations are both 
correct, the same radial canals did not supph^ these five pedicel- 
tentacles" in the two groups, Aspidochirota and Dendrochirota, 
and this would seem to indicate the separation of these two groups 
while this character was still unfixed. The origin of tentacles 
6-10, curiously enough, appears to have been fixed for all three 
groups at an earlier period. At what point the Elasipoda began 
their divergence it is hard to say, but it may have been about the 
same time as the separation of the Aspidochirota and Dendro- 
chirota. There can be little doubt that the Molpadonia were 
