II DOLIOLUM—STRUCTURE 97 
small stigmata; consequently there is a free passage for the 
water through the body along its long axis, and the animal 
swims by contracting its ring-like muscle-bands so as to force out 
the contained water posteriorly. When stigmata are found on 
the lateral walls of the branchial sac (see Fig. 59) there are 
corresponding anteriorly directed diverticula of the peribranchial 
cavity. There is a distinct endostyle on the ventral edge of the 
branchial sac and a peripharyngeal band surrounding its anterior 
end, but there is no representative of the dorsal lamina along its 
dorsal edge ; and there are neither branchial nor atrial tentacles. 
The oesophagus commences rather on the ventral edge of the 
posterior end of the branchial sac, and runs backwards to open 
into the stomach, which is followed by a curved intestine opening 
into the peribranchial cavity. The alimentary canal as a whole 
is to the right of the middle line. The hermaphrodite repro- 
ductive organs are to the left of the middle line alongside the 
alimentary canal. They open into the peribranchial cavity. 
The ovary is nearly spherical, while the testis is elongated, and 
may be continued anteriorly for a long distance. The heart is 
placed in the middle line ventrally, between the posterior end of 
the endostyle and the oesophageal aperture. The nerve-ganglion 
hes about the middle of the dorsal edge of the body, and gives 
off many nerves. Under it is placed the neural gland, the 
duct of which runs forward and opens into the anterior end of 
the branchial sac by a simple aperture surrounded by the spirally 
twisted dorsal ends of the peripharyngeal bands. 
Life-History.—The ova produced by the Doliolum of the 
sexual generation, after a complete or “ holoblastic” segmenta- 
tion, and normal invagination, produce tailed larvae with a 
relatively small caudal appendage, and a large body in which 
the characteristic musculature begins to appear (Fig. 60, A). 
These larvae after metamorphosis lose their tails and develop 
into oozooids, known as “nurses,” which are asexual, and are 
characterised (Fig. 60, B) by the possession of nine muscle-bands, 
by the stigmata being few in number and confined to the posterior 
end of the branchial sac, by an otocyst on the left side of the body, 
by a ventrally-placed complex stolon or “ rosette organ ” near the 
heart, from which primary buds are produced by constriction, 
and by a dorsal outgrowth (“ the cadophore”) near the posterior end 
of the body. The buds (blastozooids) give rise eventually, after 
VOL. VII I 
