666 



JOHN BEARD, 



formed before the embryo arises, their business is to migrate into 

 the embryo, when this is formed. Perhaps sometimes they start too 

 soon, or too far forward, or they may take the wrong path. If they 

 start too early, they may get landed and stranded in the nervous 

 system or skin: if too far forward, they come to lie, it may be, far 

 in front of the future genital region. It must be noted, that their 

 paucity in the head-region and their absence in the tail both indicate, 

 that their pathway is directly upwards from the yolk-sac into the 



embryo. If they take the 

 wrong path, they may finally 

 arrive almost anywhere. 



The germ-path is a very 

 definite one (text -figure C). 

 It is from the yolk-sac upwards 

 between splanchnopleure and 

 gut in the hinder portion of 

 the blastoderm. It is here 

 that in early stages (6 to 8 mm 

 embryos and even in larger 

 ones) a great many of them 

 are encountered in various 

 positions (Figs. 24, 26, 29, and 

 36 Ä-D). 



This pathway, which may, 

 therefore, be termed the ger- 



spl 00 BCD jjj.jj^j p^^ij l^j ^ jg^^g ^^Q^ 



^^^" ^' directly to the position, which 



they ought finally to take up in the "germinal ridge" or nidus (com- 

 pare text-figure C). 



That this is a definite track is shown 1) by the great number of 

 germ-cells in it in early stages, and 2) by the very large number — 

 the majority in fact — which have either gone to its end, or halted 

 somewhere along it. Their instinct appears to be to go along this 

 path, and then to pierce the splanchnopleure. Those which go to 

 the end and those which tarry carry out these "instructions"! The 

 former, in embryo No. 454 numbering 349, reach the germinal nidus ; 



h y 



1) Originally written "germinal track", but this term has been em- 

 ployed by Weismann in a very different sense. 



