498 
HUBERT LYMAN CLARK 
the development if possible. In later 3'ears, he expressed the hope 
that I would publish such results as I had obtained. When, there- 
fore, it was suggested that his former students publish a volume of 
zoological papers as a tribute to his memory-, it seemed to me especi- 
ally appropriate that I should prepare an account of the devel- 
opment of Chiridota, so far as the material at hand would per- 
mit. Fortunately the Bermudan material has proved to contain 
some much-desired stages, in an excellent state of preservation, 
and has thus supplemented that from Jamaica quite satisfacto- 
rily. The recent papers by Ostergren ('07), Becher ('07, '08, '10) 
and Edwards ('09) have been a further stimulus to my work, 
arousing, as they have, renewed interest in the phylogeny of holo- 
thurians. The present paper consists of two parts, one devoted 
to the account of Chiridota rotifera and its development, the 
other to the bearing of the facts there set forth, on the phylogeny 
of the class. 
PAirr I. THE XATI KAL HISTORY AND DEVELOPMENT OF 
CHIRIDOTA ROTIFERA 
Few species of Chiridota are better characterized than rotifera, 
the only member of the genus known to occur in the West Indian 
region. It was first described by Pourtales in 1851 from Florida 
specimens and is easily recognized by its small size, distinctive 
color, numerous wheel-papillae, and the minute rods in the skin. 
Although large individuals when fully extended are nearly 100 
mm. long, the great majority of specimens are less than 60, even 
when living; preserved specimens are usually 30-50 mm. in length. 
The color in life is pale flesh-red, with either a pink or a yellow 
tinge, but this ground color is obscured by the convex, white 
spots, knowm as wheel-papillae," formed by the clusters of 
calcareous wheels in the skin. These wheel-papillae are num- 
erous, often crowded, and occur all over the body; in young 
individuals, however, they may be few and scattered on the ven- 
tral side. The twelve tentacles are white or cream-colored and 
have 8-14 digits. In alcoholic specimens the colors are usually 
deepened and are fairly persistent, but after som.e months they 
