610 Bashford Dean Memorial Volume 



drawings show embryos much alike. The head of Garman's fish is thinner and is smoothly 

 rounded down to the upper jaw. Dean's specimen is thick in head and gill-region and the 

 head rounds steeply to the upper jaw. The mouth of the 64'mm. embryo is in about 

 the same stage of development as that of the 55'mm. fish. The spiracle of Carman's 

 fishlet is not so high on the head as that of the other embryo but is elongate vertically 

 and has more gill-filaments protruding. There is some slight diiference in the shape of the 

 gill-openings, but both little fish are well supplied with external filaments. Remarkably 

 alike are the fins, paired and unpaired. Both tails have about the same droop. 



In Ventral View. — Carman's full-length figure of his 64-mm. embryo in this aspect 

 is shown in Text-figure 29b. For adequate comparison we must turn to Figure 37, 

 plate III, Dean's 55-mm. specimen in ventral head aspect. Carman's embryo has the 

 mouth not quite so well developed, and the nostrils are not placed so far forward. The 

 first gill-cover in each fish is continuous across the isthmus. Carman's specimen (Text' 

 figure 29b) has a great number of short filaments protruding trom each slit. Dean's fish 

 has none showing in the figure in ventral aspect (Figure 37, plate III) although they are 

 portrayed in the lateral view (Figure 36 on the same plate). As Text-figure 29b shows, 

 the 64-mm. embryo has the pelvic fins well developed. Note the cloaca between their 

 hinder ends. Anal and caudal show in the drawing. The pectoral fins and the yolk 

 stalks look much alike. 



These drawings (Text-figures 29a and b), made on a much smaller scale than Dean's, 

 show few details. The specimen, loaned by Dr. Barbour, is before me as I write, and I can 

 testify that the little fish is accurately drawn. The inclusion oi Carman's figures herein 

 help make the transition between the 54-rmn. embryo and that now to be described. 



Dean's Embryo Measuring 66 Millimeters 



Third in the series of drawings of embryos noted above as being done by a diiferent 

 hand and at a later time, is the embryo under consideration. In the original drawings 

 this 66-mm. sharklet is enlarged to 256 mm. (i.e., is x c 3.9). Seeking a younger embryo 

 with which to compare it, I have made only secondary comparisons with Carman's 

 64-mm. specimen as being too close and because his figures show too tew details. I have 

 also passed over Dean's 55-ram. embryo which has but one full-length figure. Direct com- 

 parison will be made with the close neighbor of the 55-mm. embryo, the more typical 

 54-mm. fishlet, which like the present specimen, is portrayed in all three aspects. 



Dorsal View. — Comparison of this 66-mm. embryo with the 54-mm. specimen — the 

 former in Figure 38, plate IV; the latter in Figure 32,pla te III — shows that the 66-mm. fish 

 is plainly older. The front curve of the head is flatter, the eyes are prominent, the con- 

 striction back of the eyes is greater, but the sensory-pore system is hardly so clear. The 

 gill-covers are widely distended, and there is still a profusion of external gill-filaments — 

 but these are shorter and those in the spiracle are fewer. The differentiation in the trunk 

 region, faintly foreshadowed in the dorsum of the 54-mm. fish, is here far more clearly 



