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 reproductive 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 lies 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" segmentation, 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 {98}further division, to the sexual generation, which is polymorphic—having three distinct forms, in two of which the reproductive organs remain undeveloped. [Illustration: FIG. 60.—Life-history of _Doliolum_. A, tailed larval stage; B, "nurse" or oozooid, showing buds (blastozooids) migrating from the ventral stolon to the dorsal process; C, posterior part of much later oozooid to show buds arranged in three rows on dorsal process; D, stolon segmenting; E, young migrating bud; F, trophozooid developed from one of the buds of a lateral row. _At_, Atrial aperture; _b_, buds; _Br_, branchial aperture; _cl_, cloaca; _d.p_, dorsal process; _end_, endostyle; _ht_, heart; _l.b_, lateral buds; _m.b_, median buds; _n.g_, nerve-ganglion; _ot_, otocyst; _p.c_, pericardium; _sk_, stalk; _sto_, stolon. (After Uljanin and Barrois.)]