Figure 20_d_ represents a section through the hindbrain (_hb_), pharynx (_ph_), and tip of the snout. On either side of the hindbrain are a convoluted auditory vesicle (_o_), and several blood-vessels and nerves, while ventral to it is seen the anterior end of the notochord (_nt_), around which the mesoblast is somewhat more dense than elsewhere. The pharynx (_ph_) sends out toward the surface a narrow gill cleft (_g′_) in the neighborhood of each auditory vesicle. These clefts connect with the exterior by very narrow slits, not seen in the plane of this section. The opposite end of the pharynx, as seen in this figure, opens on the left (_pn_) into the nasal chamber. The nasal cavity on the right is cut in such a plane that it shows neither its external nor its pharyngeal opening. The nasal passages are here fairly long and nearly straight chambers; their lining epithelium is quite thick in the middle region, but becomes thinner where it merges into the epithelium of the pharynx at one end, and into the superficial epithelium at the other end. The unusual appearance of the eye (_e_), on the right side of the figure, is due to the fact that the plane of the section cut tangentially through the extreme edge of the eye in the region of the choroid fissure. Figure 20_e_ is only a short distance posterior to the preceding. On the left side the pharynx (_ph_) is connected with the exterior through the stomodæum, and on the right the hyomandibular cleft (_g′_) is cut almost through its opening to the exterior. The auditory vesicle (_o_) on the right is cut near its middle region, while that on the left is barely touched by the plane of the section. The notochord (_nt_), with its condensed area of mesoblast, is somewhat larger than in the preceding section. The nasal canal on the right (_n_) is cut through neither anterior nor posterior opening, while on the left side the canal shows the anterior opening (_an_). Figure 20_f_, which is in the region of the posterior part of the pharynx and the anterior part of the heart, shows some rather unusual conditions.