BULLETIN OF THE UNITED STATES FISH COMMISSION. 301 



current is from the bead to the tail. There are already over 80 muscular segments 

 formed, and the hreast-fm is developing at/. 



Fig. r2.— Embryo, 94^ hours okl, viewed as a transparent object. The uotochord 

 is shown as a broad bbick line, and the lateral yelk-vessels v' v" are much more de- 

 veloped than in Fig. 11. 



Fig. 1:3. — Diagram to show the origin of the mode of anastomosis of the larger ves- 

 sels, enlarged 52 times. 



EXPLANATION OF PLATE XXI. 



Fig. 14. — Embryo silver gar, 116 hours and 40 minutes after impregnation, showing 

 the further development of the heart and blood-vessels traversing the surface of the 

 yelk. Those on the opposite side of the yelk are indicated by the dotted lines. Pig- 

 ment cells have made their appearance on the body beneath the superficial epiblast 

 and on the yelk and the heart. The intestine and urinary vesicle b are well devel- 

 oped, as seen in the tail end of the embryo on the opposite of the egg through the 

 vitellus. 



Fig. 15. — Sketch of heart and vessels which, empty into it in an embryo 140 hours 

 old; the formation of the blood is in active progress where the vessels converge to 

 join the heart, which is now blotched with pigment cells of two colors in life. En- 

 larged 2(3 times. 



Fig 16. — Embryo silver gar, viewed from the side as a transparent object 165^ hours 

 after impregnation, to show the progress of development of the blood vessels over the 

 yelk on the right side. The heart or pericardiac cavity j) is now enormously devel- 

 oped, and the development of blood cells is going on with great activity in its lower 

 part, where the venons end a of the heart is attached. The heart itself is now greatly 

 elongated downwardly, and is one-third as long as the whole embryo. 



ON THE REARIIV« OF IV'HITEFI.SII IN SPRING-WATER AND ITS 

 REI^ATION TO THEIR wrRSEQUENT HBSTRIRrTION. 



By FRANK N. CLARK. 



[Letter to Prof. S. F. Baird.] 



I am not preiDared to say whether or not eggs of the whitefish are 

 prematurely hatched in spring-water. I take it that the question is a 

 scientilic problem for scientists to solve; that it is a point on which 

 even " doctors disagree." 



If we could "reaj) what we sow" from our plants of fish in bodiesof water 

 like the great lakes we would soon have a practical test of the respective 

 value of "premature" or "retarded "development of eggs or embryos; but 

 this is impossible, and so if there is any difference we must detect it 

 from evidence that is circumstantial or theoretical. It seems reasonable 

 to assume that if the little fellows are vigorous when hatched, whether 

 of three or five months' incubation, and are released when and where 

 aliment for their sustenance is abundant, a large percentage of those 

 not destroyed by predaceous fishes ought to become adults. There is 

 no difference in size and activity between fish brought out in three or 

 six months, where the same water is used ; neither are there points 

 about the former that can be construed into evidence of abnormal de- 



