612 Bashford Dean Memorial Volume 



When Figure 40, plate IV (the 66'mm. embryo) is compared with Text-figure 29b 

 (Carman's 64'mm. specimen), it is plainly seen that the two embryos are very much like 

 each other. The heads are alike broad and blunt. The distance from the center of the 

 upper jaw to the tip of the snout in the 66'mm. specimen is shorter than in the other. 

 The first gill-covers in each are confluent across the isthmus — with a blunt backward 

 central point in Figure 40, plate IV, and a straight line across in Text-figure 29b. Both 

 heads in this aspect show a profusion of external gill-filaments in each gill-opening. In 

 the 66-mm. embryo, there is seen the beginning of the tropeic folds reaching from yolk 

 stalk to cloaca. Nothing of the sort is to be seen in the 64-mm. fish. 



An Embryo 103 mm. in Length 



This embryo, the last of the new lot of four drawn in three aspects, is about one and 

 one-half times the length of the 66-mm. fishlet, but in the original drawing it measures 

 approximately the same — 257 mm. (i.e., x 3.9). 



Seen from Above. — The merest glance shows that this 103-mm. fishlet (Figure 41, 

 plate IV) has advanced much over the preceding stage (Figure 38, plate IV). The head is 

 smaller, more compact, more finished looking. The latero-sensory canals are well develop- 

 ed. The spiracles are so reduced in size that the external openings are barely visible. The 

 gill-covers are far less distended than in the 66-mm. fish, and the filaments are somewhat 

 fewer but generally longer. The paired fins show marked growth and the dorsal is some- 

 what in evidence. 



In Lateral Aspect. — Seen in side view (Figure 42, plate IV) and in contrast with the 

 like aspect of the 66-mm. specimen, it is apparent that the larger embryo has gone forward 

 markedly in development. It now begins to look like the adult. Note the pointed snout 

 and the long mouth with the fold above, marking off the jaw cartilage. Eye and nasal 

 opening are in their normal positions. All the gill-covers are for the first time distinctly 

 frilled. The external gill-filaments are still persistent. The lateral-line and head-canal 

 systems are continuous. The fins, paired and unpaired, are well developed. The tail is 

 straight and the lower lobe of the caudal has a faint notch near the tip. The little shark 

 begins to look snake-like — anguineus. 



Seen from Below. — In this aspect the 103-mm. fish (Figure 43, plate IV) looks more 

 developed than does the 66-mm. embryo (Figure 40, plate IV). The head is narrower and 

 more pointed. The mouth is slightly narrower and the lower jaw considerably longer — it 

 distinctly recalls that of the adult. The gill-covers (especially the first pair) are seen to 

 be frilled. They are less distended than those on the heads previously studied. The 

 external gill-filaments persist and protrude. Both the paired fins, the pectorals especially, 

 show much development. The cloacal opening looks as though it might be functional, 

 and the abdominal pores are prominent. On the mid-line of the ventral trunk is the 

 tropeic ridge and on either side the somites show distinctly. 



An Embryo of 124 Millimeters 



Having finished the study of the later-portrayed series of embryos shown each in 

 three full-length drawings, we will now proceed to a consideration of some figures of 



