stage VIII 



At the beginning of this str.ge tho developing tail is free fron the 

 yolk mass for a length greater than tho length of the hcadj by the end 

 of the stage about one-third of the body at the tail end is separated 

 fro"i the yolk. The fin-fold is bccnning conspicuous, although it is b-i-'oly 

 half as Vifide as the enbryo by the end of, the stage. The intestine can 

 be seen as a line along the ventral side of the developing tail, and tho 

 position of the vent is indicated in the fin-fold. Somites are formed 

 along the tail, at least as far as the end of the intestine. - The tail 

 tapers posteriorly, but the tip is still rounded. 



Stage IX 



Approximately one-third of the body is free from the yolk at the 

 beginning of the stage and the tail is often bent- to one side^ by the 

 end of the stage the tail is always curved, either to the right or left 

 of the yolk, and comprises about f/ro-fifths of the total length of the 

 embryo. The fin-fold is about hair as v/ido as the body at the beginning 

 of this stage, it is somevThat broader along the free ventral portion of 

 the body than along the dorsal side; by the end of the stage the ventral 

 fin-fold is nearly as vjlde as thvi body proper, During stage IX pigment 

 spots (melanophores ) may appear on the dorsum in two parallel rov/s, one 

 on either side of the notochord, with the spots more niuiierous ii-.mediately 

 behind the headj on some specimens pigmentation does not appear until 

 after this stage. The embryo conforms less to the shape of the yolk 

 than previously and is beginning to straighten in its middle portion; 

 at tho end of- this stage the tail is curved to one side of the yolk at 

 about a U5'^ angle to the plane of the embryo. 



Stage X 



The free tail comprises at least tvro fifths of the length of the 

 body at the beginning of the stage and is as long as the remainder of 

 the body by the end of the stage. During stage X a fundamental change 

 in the orientation of the embryo is completed, a change bugun in the 

 previous stage. This is accomplished by the straightening of the body 

 of the embryo and the upward flexing of tho tail. The embryo as a whole 

 is no longer curved aro\ind the yolk; rather the plane of orientation has 

 been rotated a con^leto 90°, Only the head end remains curved around 

 the yolk, the remainder of the body being straightened out into one plane, 

 although it is U-shaped due to the flexing of the end of the t^il? During 

 this stage the tail increases, in length, until its tip is nearly as far 

 forward as the base of the head; the fin-fold is about as wide as the body 

 along the dorsal side and somev/hat i/ider along the ventral margin. 



Stage XI 



This is the last stage before hatching. At the beginning cf the stage 

 the tail stretches as far fonrard as the base of the head, and the pos- 

 terior portion of the body free from the yolk sac is longer than the por- 

 tion carrying the yolk sac, and this disparity increases during tho stage. 



150 



