. The elasmobranch fishes. Chondrichthyes. 298 THE ELASMOBRANCH FISHES leeted in tlie median vesicles at the end of the segmental duct (see fig. 254a, ) and there appeared as large colored patches. In no specimen did the ink or carmine which entered the nephrostome gain access to the tissue of the kidney. DEVELOPMENT OE NEPHKOSTOME AND SEGMENTAL DUCT A section through the body cavity of an embryo of Heterodontus francisci (fig. 257) cuts through the nephrostome or funnel (nph.). If traced farther back, it would be found that this funnel by means of the segmental duct joins the pronephrotic
. The elasmobranch fishes. Chondrichthyes. 298 THE ELASMOBRANCH FISHES leeted in tlie median vesicles at the end of the segmental duct (see fig. 254a, ) and there appeared as large colored patches. In no specimen did the ink or carmine which entered the nephrostome gain access to the tissue of the kidney. DEVELOPMENT OE NEPHKOSTOME AND SEGMENTAL DUCT A section through the body cavity of an embryo of Heterodontus francisci (fig. 257) cuts through the nephrostome or funnel (nph.). If traced farther back, it would be found that this funnel by means of the segmental duct joins the pronephrotic duct (). At first the most anterior of such funnels may pro- vide a passageway from the body cavity to the pronephrotic duct, but later the most anterior of these fuse into a single enlarged funnel. Those segmental funnels arising back of this have segmental ducts (, fig. 258) which join the pronephrotic duct only secondarily. In the segments farther back, however, each segmental duct of Acanthias grows from its funnel laterally, enlarging into a median vesicle (, fig. 258a) . From this it may even continue inward to join an outgrowth from the pronephrotic duct (). The following structures are found in order from the funnel or nephro- stome to the pronephrotic duct: (1) the nephrostome (nph.); (2) its segmental duct (); (3) a median vesicle () which supplies the tissue for Bowman's capsules; (4) the tube leaving the capsule which becomes the renal tubule (); and (5) the primitive collecting tubule () which according to Borcea (1906) buds off from the pronephrotic duct and later lengthens out into the collecting tubule of the adult. At this point in its development, connection is made from the nephrostome to the pronephrotic duct (ScylUnm, fig. 256), and it is not impossible that while this temporary connection lasts nitrogenous waste may pass from the body cavity through the pronephrotic (now the Wolffian) duct and out through the cloaca. But
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