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HUBERT LYMAN CLARK 
presence of ciliated bands and wheel-shaped deposits, and in the 
absence of a mouth. 
3. The pentactula larva of Chiridota differs from that of Syn- 
aptula in the presence of traces of ciliated bands, an atrial collar, 
wheel-shaped calcareous deposits, and square-tipped or sUghtly 
bifid tentacles. 
4. The calcareous wheels developed in the larvae of Chiridota 
resemble in their development, in the number of spokes, and in 
certain details of structure, those which are found in adults of 
Trochoderma, and are essentially different from the true Chiri- 
dota-wheels, which appear after the pentactula stage. Whether 
the auricularia larva, with similar Trocho derma-like wheels, 
found at Naples by Semon and considered by him to be the young 
of Labidoplax digitata, really belongs to that species, must be 
considered still an open question. 
5. The development of Chiridota, though accelerated by its 
viviparous habit, is apparently not so rapid as that of Synaptula. 
This is indicated by the later formation and anterior position of 
the atrium, the much later formation of the mouth, and the more 
deliberate formation of the second quintet of tentacles. 
6. The viviparous habit appears to have been acquired by 
Chiridota much more recently than by Synaptula. This is indi- 
cated by the much larger number of young in a brood, by their all 
being of a single age, by their slower development, by their appar- 
ently earlier birth, by the retention of the ciliated bands of a free- 
swimming auricularia stage, by the unequal development of the 
secondary tentacles, producing seven- and eight-tentacled larval 
stages, by the more conspicuous and persistent ''anterior coelom," 
and by the absence of larval ''glandular organs." 
PART IL THE PHYLOGENY OF THE HOLOTHURIANS 
In any discussion of the phylogeny of a class of animals, we 
ought to distinguish so far as possible between the interrelation- 
ships of the groups which make up the class, and the relationships 
of the class as a whole with other classes. Among Echinoderms 
this can easily be done, for not only is the phylum a remarkably 
