218 HIROSHI OHSHIMA 
13. MeraDOLIOLARIA. 
Near the end of the doliolaria stage many important changes 
occur internally, though but few changes are seen from the 
outside. When seen externally, the pre-oral hood gradually 
diminishes in size, and in consequence the tentacular crown 
shifts anteriorly, calcareous deposits appear while the ciliary 
bands degenerate, and the tentacles and pedicels become 
prominent and visible from the outside. The internal changes 
are: the further development of the hydrocoele appendages 
into the adult water-vascular system, the differentiation of 
musculature and nervous tissue, the widening of the enterocoele, 
&e. This I may call the metadoliolaria stage. The larva now 
very often sinks to the bottom from its increased specific gravity 
and degenerated ciliary function. 
Water-vascular System.—As was stated by Lud- 
wig and Newth, the ring canal lies a little obliquely in such 
a direction that its dorsal half approaches the anterior end of the 
body rather more than the ventral, but I could not find any 
lateral inclination such as was observed by Ludwig, who 
stated that the left half is slightly more posterior than the 
right (22, p. 181). 
In my culture the tentacles begin to protrude a very little 
above the surface of the body at the end of the fourth day, 
and early in the morning of the next day a slow movement 
was observed, obviously owing to the differentiation of muscle 
fibres in their wall. The tip is found coyered with minute hyaline 
papillae as known to Selenka, Ludwig, and_ others 
(Text-fig. 5, p). The ramification occurs on the seventh day. 
The primary pedicels now protrude as short cylindrical promi- 
nences, as clearly seen in the sixth-day larva. 
Musculature.—Longitudinal muscle fibres are now to 
be found below the hydrocoele epithelium in the tentacles and 
pedicels, and along the radial canals. They appear in the ten- 
tacular wall first along the internal (axial) side and then spread 
around the cavity. Those of the radial canals le along the 
