DEVELOPMENT OF CUCUMARIA ECHINATA 205 
end but often reverse, which latter movement makes the larva 
sink to the deeper part of the water. Besides these two kinds 
of locomotion, rotation around the body-axis is observed at 
the same time. In no ease is the pre-oral hood directed down- 
wards, 
Although no marked change is visible externally, the latter 
half of the stage had better be treated under a distinct heading, 
Metadololaria, owing to its internal changes. Here in the 
present chapter I will confine myself to the earlier part, doliolaria 
in the narrow sense. 
In the corresponding stage of C. frondosa, Danielssen 
and Koren (11) found that rudiments of the tentacles appear on 
the tenth day and a pair of the primary pedicels on the twentieth. 
Des Arts (2, p. 9) observed in the same species that the larva 
measures on the fifteenth day 510 by 875, and that the 
tentacles are visible in section on the twenty-first day, but are 
observable externally so late as on the twenty-fourth day, and 
the pedicels make their first appearance on the thirty-seventh 
day. The internal structure of the doliolaria of C. kirchs- 
bergii was described and figured by Kowalewsky (1%, 
fig. 12). The same author gave an external view of the larva 
of C. planci (figs. 16, 17), while Selenka (45) and Ludwig 
(22) made much closer observations. From the observations of 
Newth (86), we gather that the corresponding stage in 
CU. saxicola and CO. normani is not distinguishable 
externally from lack of the ciliary bands which are so charac- 
teristic of the stage in other species. 
Ciliation of the Eetoderm.—tThe presence of three, 
very rarely four, transversely-running bands of cilia is a very 
marked character of doliolaria. They seem to appear simul- 
taneously. The most anterior band lies about on the middle 
of the body (PI. 9, fig. 25, ¢,), the second and third run parallel 
to the former and in such a way that they divide the posterior 
half of the body into three equal divisions, or, as is often the case, 
the hindermost third is a little broader than the other two 
(¢y-3). In preserved specimens the cilia are extremely difficult 
to make out, but they can easily be found in the living state. 
