into the Growth of the Blastoderm of the Chick. 351 



kind, such as that of Professor Oscar Hertwig, who studied the 

 various monstrosities obtained by mechanical compressions, by super- 

 maturation of the ovum, and addition of various salts to water in 

 which the eggs were developing. Similar work has been done upon 

 sea-urchin's eggs by several biologists (Pouchet and Chabry, Herbst, 

 <fcc.). 



There are other most valuable records of the results obtained by 

 separating the several spheres of the early stages of segmentation of 

 eggs of Ctenophores, Echinoderms and Amphioxus by Chun, Driesch, 

 Wilson, and others. 



Kastschencko, by injuring portions of the germ ring of Elasmo- 

 branch embryos, has produced very valuable evidence in connexion 

 with the concrescence theory, and Morgan has by similar methods 

 examined the development of Teleosteans. 



As far as I know, an experimental study of the development of the 

 avian blastoderm has not hitherto been made. 



The method adopted, which is very simple, was as follows. The 

 egg was first of all opened at one side, and a bristle inserted into the 

 yolk at some distance away from the blastoderm, to mark its anterior 

 and posterior axis. 



The yolk, with its surrounding albumen, was then turned out into 

 a glass vessel having a rather greater capacity than that of an ordinary 

 egg shell. 



The yolk was arranged so that the blastoderm floated uppermost, 

 and a wire or celluloid ring was placed over it to prevent the yolk 

 from floating to the surface. 



A fine sable hair was then inserted in the blastoderm, and its posi- 

 tion measured by a micrometer eye-piece and recorded in tenths of a 

 millimetre. The vessel was filled up with albumen and covered 

 with a glass lid, and placed in the incubator at a temperature of 

 104 F. 



Under these conditions, although development was slower than 

 under normal conditions, many embryos reached, after about forty- 

 eight hours, an age equivalent to a normal thirty to thirty-six 

 hours' chick with nine or ten pairs of mesoblastic somites. . }crJ< 



To come now to the results of the experiments, it is clear that if 

 Duval's theory is correct a hair inserted in the area opaca at the point 

 a (fig. A (i)) ought to appear, in a specimen in which the primitive 

 streak is formed, somewhere in front of the primitive streak. It, 

 however, does not ; it appears in the area opaca behind the primitive 

 streak at a, fig. A (ii). 



So again if the primitive streak is formed by the concrescence of 

 the posterior margin, the sables inserted at the posterior edge at XX 

 should either appear in the primitive streak or else prevent its 

 formation. 



