(4) The growth downwards of the muscle-plate to form the muscles of the abdomen.
(5) The formation of an outgrowth on each side of the mesentery (pov), which will become the ovary.
(6) The spiral valve (al).
Fig. 14. Transparent view of the head of an embryo shortly before the appearance of the external gills. (Magnified 20 diam.) The chief points to be noticed are—
(1) The relation of the cranial nerves to the visceral clefts and the manner in which the glosso-pharyngeal (gl) and vagus (vg) are united.
(2) The remnants of the pleuro-peritoneal cavity in the head (pp).
(3) The eye (op). The stalk, as well as the bulb of the eye, are supposed to be in focus, so that the whole eye has a somewhat peculiar appearance.
EXPLANATION OF [PLATE ]5. (VI. p. 112.)
Complete List of References.