478 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Plate CXV. 
Fig. 162. Outlines of ;i sagittal section of a larva about 1’9 nun. long, to show the relative positions of 
the liver, air-bladder, and yolk. 
Fig. 163. Cross-section of a similar larva through the .air- bladder. 
Fig. 161. Another section a little farther back. 
Fig. 165. Sagittal section through the midgut of a larva 2'5 mm. long. The yolk is reduced and the 
liver much more highly developed. The bile sac is just forming. 
Fig. 165a. An enlarged sagittal section through the anus and nephridial opening of a larva 3'2 mni. 
long. The rudiments of the reproductive organs are seen in po. 
Fig. 166. Sagittal section of alimentary tract of larva 3-2 ium. long. Posterior part on right below. 
Fig. 166a and b. Some of the cells of the hind-gut enlarged. 
Plate CXYI. 
Fig. 167-171. A series of sections from the same larva as fig. 166. The sections are successively nearer 
the lateral surface of the embryo. These sections show the relation of the liypoblastic 
evaginations to each other at varying distances from median plane. The gill-structures 
do not yet meet below and are not visible in iig. 166. 
Fig. 167. Several sections removed from 166. 
Fig. 168. The next section, showing the mandibular, spiracular, and three gill evaginations. 
Fig. 169. The next section, the mandibular, spiracular, and hyobrauchial not connected by hypoblast 
laterally. 
Fig. 170. Two sections removed from 169. 
Fig. 171. Two sections removed from 170. 
Figs. 171a-174a. Cross-sections through the thyroid and gill regions of a larva 3-2 mm. long. (Figs. 
173, 174 are on plate cxvii.) 
Fig. 171a. Cross-section of the thyroid gland. 
Fig. 1715. Through the same one section behind 171a. Showing connection with hypoblast cells. 
Fig. 172. Oblique section through spiracle on left and just behind hyobrauchial on right. 
Plate CXVII. 
Figs. 171a- 174a. Cross-sections through the thyroid and gill regions of a larva 3 - 2 mm. long. (Figs. 
171a, 172 are on plate cxvi.) 
Fig. 173. Six sections behind 172; the right through the posterior part of the auditory capsule, the 
left through the hyobrauchial . 
Fig. 174. Through the posterior part of the gill region ; the left through the upper (posterior) part of a 
gill pocket, the right through the anterior (lower) of another. Ciliated region of the gullet. 
Fig. 174a. Lateral margin of the gullet, two sections farther back. 
Fig. 175. Right half of a horizontal section of a larva 2 - 5 mm. long. All the gill-slits potentially 
complete. 
Figs. 176-178. Three parallel sections; 176, sagittal of a larva 4 mm. long; the mouth not yet open; 
some of the posterior gill-slits open. The ciliated gullet highly differentiated from the 
other alimentary region. 
Plate CXVIII. 
Figs. 179-183. Development of gills as seen in living larv;e viewed as transparent objects. 
Fig. 179. Larva, 0 - 9 mm. long. 
Fig. 180. Gill region of a larva 2'5 mm. long. 
Fig. 181. A little older larva, showing the mandibular and hyomandibular slits and their relations to 
the hyobranchial and succeeding slits. 
Fig. 182. Gill region of a larva 4 - l mm. long. X 2. 
Fig. 183. Gill region of an older larva in which the conditions seen in figs. 94-100 are approached. 
