368 ARTHUR E. SHIPLEY. 



one days old. a. Anus. p. g. Solid postanal gut. n. Notocbord. sp. c. 

 Spinal cord. pr. Primitive streak, y. c. Yolk-cells. 



Fig. 21. — A longitudinal section through side of head of seventeen days' 

 embryo, showing the first three evaginations to form gill-clefts, and the true 

 head-cavities, au. Ear. hd. c' . and hd. c". The first and second head-cavity. 

 br^., br^., and 6r^. The first rudiments of gill-clefts, br. v. The vessels of 

 gills, si. Stomodseum. Zeiss's A, oc. 3. 



PLATE XXVII. 



EiG. 22. — A longitudinal section through side of bead of a larva twenty- 

 one days old. au. Ear. e. Eye. br^., br"., br^., br*. The first to fourth 

 primary gill-clefts. h. b. Hind-brain, oph. Ophthalmic ganglion. V. g. 

 Ganglion in main branch of fifth nerve. 



Fig. 23. — A median longitudinal section through the head of a larva twenty- 

 one days old. pin. Pineal gland, op. ch. Optic chiasma. inf. Infundibulum. 

 n. Notocbord. st. Stomodseum. br''. Second primitive gill-cleft, th. Thyroid 

 gland, na. Olfactory invagination, pit. Pituitary invagination, m. b. Mid- 

 brain, h. b. Hind-brain. g. Groove between mid- and hind-brain. /. t. 

 Lamina terminalis. 



Fig. 24. — Transverse section through the body of a larva of twenty days. 

 sp.c. Spinal cord. f.g. Fore-gut. n. Notocbord. som.pl. Somatopleure. 

 sp.pl. Splanchnopleuric layers of myomeres. b. c. Body cavity, h. Heart. 

 c.f. Ciliated funnel, s. d. Segmental duct. Zeiss's A, oc. 3, cam. luc. 



Fig. 25. — Transverse section through trunk of larva about twenty-four days. 

 Letters as in Fig. 24, and ao. Aorta, a. c. Anterior cardinal, d. m. Dorsal 

 mesentery. sp. gl. Spinal ganglion, gl. Glomerulus. Zeiss's C, oc. 1, 

 cam. luc. 



Fig. 26. — Section through embryo, one day before hatching, seventeen days 

 old, cut whilst in the egg-shell, h Heart, sp.pl. Splanchnopleure. sm.pl. 

 Somatopleure. br' . and br^. Seventh and eighth gill-clefts, hd. Head-cavities 

 behind these, y. c. Yolk-cells, m. g. Mid-gut. b. c. Body cavity, Zeiss's 

 A, oc. 3, cam. luc. 



Fig. 27. — Longitudinal horizontal section through a larva about twenty-two 

 days. br^. — br^. The eight primary gill-clelts. br. v. Vessels of gills, br. b. 

 Branchial bars. /.^.Fore-gut. ^k^. Tubule of pronephros. ««?. Stomodseum. 

 V. Velum, g. n. Ganglion cells at base of nasal invagination. op. ch. Optic 

 chiasma. inf. Infundibulum. v.f b. Cavity of fore-brain, n. Notocbord. 

 Zeiss's B, oc. 1, cam. luc. 



Fig. 28. — Longitudinal horizontal section through larva of thirty-six days, 

 u. I. Upper lip. v. Velum, th. Thyroid gland, v. ao. Ventral aorta, ven. 



