746 Bashford Dean Memorial Volume 



bases, than in the preceding stages. Cartilaginous fin rays are indicated in both dorsal 

 fins, also in the pelvic fin. 



An embryo in the same stage of development as the one represented in Figure 35, 

 plate III, was found in Dean's collection. It measures about 50 mm. (2 inches) in length. 

 Its external gill-filaments are abundant and resemble those shoum in the figure. 



The embryo portrayed in Figure 36, plate III, is obviously older. This is sho^^Ti by 

 the marked development of the cartilaginous fin rays and by the increased size of the 

 cranium. Due to the persistence of the cephalic flexure, the mouth opening still faces 

 caudad as well as ventrad. The spiracular cleft, situated just behind the eye, is shown 

 more distinctly than in the preceding figure. Indistinct myomeres, extending to the 

 extreme tip of the tail fin, are indicated in the posterior half of the figure. This embryo is 

 remarkable for the entire absence of external gill-filaments — a deficiency that is more 

 striking when we observe that both the preceding and the following stages show a luxu- 

 riant development of these filaments. There is an indistinct lateral line. 



Figure 81, plate VII, represents fin color) an embryo only sHghtly older than the 

 one just described. This beautiful figure is noteworthy in several respects. First, it 

 shows the extreme development of the external gill-filaments; second, a tuft of these 

 comprising about 9 or 10 filaments protrudes from the spiracular cleft; third, the figure 

 represents the oldest embryo in which the eye is knov.Ti to possess a chorioid fissure; 

 fourth, it shows a rudimentary supraorbital ridge; fifth, the pelvic fin appears to possess 

 a rudimentary myxopterygium ; and sixth, the figure shows the entire yolk sac. 



Figure 37, plate III, is noteworthy for the size of the external gills, which are as 

 long, and almost as abundant, as those in the embryo just considered. In some features, 

 the embryo portrayed in this drawing is decidedly more advanced in its development. 

 This is particularly true of the mouth region. The cephaHc flexure has unbent to a degree 

 that brings the mouth into nearly its adult position. This change is accompanied by 

 increased depth of the branchial and pectoral regions, so that the profile of the ventral 

 surface is straightened (cf. Figure 36, plate III). Only five gill-filaments protrude from the 

 spiracular cleft. Structures in the branchial and pectoral regions are obscured by the 

 gill-filaments. There is a supraorbital ridge, best developed at its posterior end. Some 

 of the fins are larger than in the preceding stages. The lateral Hne is indistinct. 



An embryo in Dean's collection appears to be identical with the one represented in 

 Figure 37, plate III. It is about 70 mm. (2.75 inches) long. .Another embryo, in Dean's 

 collection, which appears sHghtly more advanced in its development, measures only 

 about 60 mm. (2.36 inches) in length. Its external giU-filaments have reached their 

 maximal development. 



The embryo portrayed in Figure 38, plate III, shows important changes. The head, 

 including the branchial region, has increased in depth so that in side view the embryo is 

 shaped more Hke a tadpole. Through a sort of telescoping of the branchial and pectoral 

 regions, the three posterior gill-clefts have come to He dorsal to the base of the pectoral fin, 

 as in the adult. The distance between the spiracular cleft and the first gill-cleft has 



