PROBOSCIS PORES ” IN CRANIATE VERTEBRATES. 553 
bular somite, pos. Preoral sense-organ, rbc. Roof of buccal cavity. 
rbf. Riglitoral hood, rc. 1 and rc . 2 Right first and second ccelomic cavities. 
rs . 1 and rs. J Right first and second coelomic sacs or somites, ve. Ectoderm 
ventral to preoral pit. 
PLATE 28. 
Figs. 1-14 are of Amphioxus. 
Fig. 1. — Transverse section through anterior region and neuropore 
of a 24 hours’ old embryo. Cam. W., 2 mm., oc. 3. 
Fig. 2. — Similar section through a more advanced embryo, 24 hours 
old. Cam. W., 2 mm., oc. 3. 
Figs. 3 and 4. — Transverse sections through an embryo 24 hours old. 
Fig. 3 shows the anterior somites, fig. 4 only the second pair of somites. 
Cam. W., 2 mm., oc. 3. 
Fig. 5. — Transverse section through an embryo 30 hours old. Cam. 
W., 2 mm., oc. 3. 
Fig. 6. — Transverse section through a larva 48 hours old, with 
Hatschek’s pit opening to the exterior. Cam. W., 2 mm., oc. 3. 
Fig. 7. — Portion of a transverse section of a larva with two open 
gill-slits, showing Hatschek’s pit and the preoral sense-organ. Cam. 
W., 2 mm., oc. 3. 
Fig. 8. — Transverse section of an older larva. Cam. W., 2 mm., oc. 3. 
Fig. 9. — Portion of a transverse section of an older larva, showing 
the developing preoral pit and groove. 
Fig. 10. — Section of the same larva farther forward. Cam. W., 
2 mm., oc. 3. 
Fig. 11. — Portion of a transverse section of the buccal region of an 
old larva in which the atrium has developed. Cam. W., 2 mm., oc. 2. 
Fig. 12. — Longitudinal vertical section through Hatschek’s pit in an 
adult. Cam. Z.D., oc. 2. 
Fig. 13. — Transverse section through Hatschek’s pit in an adult. 
Cam. Z.D., oc. 2. 
Fig. 14. — Enlarged view of a portion of a section of the epithelium 
lining Hatschek’s pit in the adult. 
Fig. 15. — Portion of a transverse section of the head of an embryo 
of Torpedo 10*5 mm. long. The entrance of the premandibular tube 
or canal, ca, into the hypophysis is shown. 
VOL. 62, PART 4. NEW SERIES. 
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