C.l.YCOdKX IN Till-: CHICK KMMUVO. 65 



nervous system and in the ectoderm below the hcadfold (Fig. 3). 



As soon as the heart tissue begins to develop (at about twenty- 

 eight hours) it takes on its glycogenic function and from that 

 time to the oldest embryos studied the heart is the most con- 

 sistently and by far the most abundantly glycogenated organ of 

 the body. The glycogen here appears in very deeply stained 

 granules embedded close together throughout the muscular 

 walls of the entire heart, and extending into the sinus venosus 

 and the bulbus. Fig. 4 shows, in stippling, the position of the 

 glycogen in the heart tubes of a chick of nine somites. Fig. 5 

 shows a part of the heart of a six-day chick, with glycogen abun- 

 dant in the muscles. Fig. 50 represents a part of the wall of a 

 four-day chick's heart, and Fig. 56 of a ten-day chick's heart, 

 under high power. In both of these the actual globules of glyco- 

 gen have been represented in black. 



The glycogen of the vascular area seems to be continued under 

 the embryo with more or less regularity. Certainly as the 

 gut is formed glycogen extends into it, appearing in some cases 

 very distinctly at the opening of the gut onto the yolk, more 

 abundant at the opening of tl\v, hind-gut than of the foregut, 

 extending in a thirty-five-hour chick into the pharynx, and from 

 fifty-six hours on being very noticeable in the intestine. Fig. 6 

 shows the fore-gut of a four-and-a-half-day chick just in front 

 of the anterior portal. The glycogen in the entoderm of the 

 gut and below it is stippled. Fig. 7 is the posterior intestinal 

 portal of a seven-day chick, and Fig. "ja is the intestine and 

 splanchnic entoderm of the same a few sections posterior to 

 Fig. 7. Fig. 8 is a transverse section through the intestine of a 

 ten-day chick, showing glycogen abundant in the epithelium. 



At fifty-six hours, and in all later stages, glycogen was found 

 in the myotomes, being particularly striking in those sections 

 where the body was cut sagitally, the glycogen here appearing 

 like mahogany-colored beads on the spindle-shaped myotomes 

 (Fig. 10, Plate II.). F'g. 9 (Plate II.) is a transverse section of 

 a chick of five days showing the position of the glycogen in the 

 myotomes. Under high power one of these myotomes appeared 

 as in Fig. II, where the actual spots of glycogen are represented. 

 As other muscular parts develop the myotomes become less 



