Experimental Studies on Germinal Localization. 1 1 



widely so as to appear as a general thickening of the ectoplasmic 

 layer over the whole upper hemisphere (Figs. 12, 13). This 

 thiclcening is most marked near the animal pole, where it is very 

 conspicuous at the time of cleavage, extending thence approxi- 

 mately to the equator of the egg, or slightly below it, but without 

 any very definite margin. It stains deep red in Congo red and 

 shows a finely alveolar structure quite unlike that of the original 

 disc. 



During the foregoing stages marked changes occur also in the 

 lower protoplasmic area, and it is evident that active movements 

 of its material take place. These are perhaps due in part to the 

 entrance of the spermatozoon at the lower pole, but in part also 

 to the fact that upon the breaking down of the germinal vesicle 

 the finely granular material derived from It becomes more or less 

 definitely confluent with the lower area (as Wheeler describes 

 in Myzostoma) , so that an irregular pillar of protoplasm, sur- 

 rounded on all sides by yolk, now extends from the lower pole 

 nearly to the upper protoplasmic area (Fig.ii) and ultimately 

 becomes connected with the latter as the first maturation spindle 

 moves upwards.^ In vertical section it may very clearly be seen 

 that the material of the upper part of this pillar differs markedly 

 from the lower, both In texture and in staining capacity (the two 

 regions show a rather distinct boundary, indicated by the dotted 

 line in Fig. 11), the lower region being very dense and staining 

 in the double stain clear red, the upper one much looser (alveo- 

 lar?) in structure and staining purple or blue. During the polar 

 body formation the lower area changes its form, often becoming 

 irregular and sometimes elongate or sickle-shaped. It is a note- 

 worthy fact that at the time each polar body Is extruded the egg 

 becomes irregular in contour or almost amoeboid, at the center 

 of the loiier polar area, afterwards resuming Its even outline.^ 

 After formation of the polar bodies the upper part of the proto- 

 plasmic pillar retreats from the periphery, while the yolk again 

 extends across the upper region above the egg-nucleus. In the 

 upper part of the internal protoplasmic region conjugation of the 



1 Cf. Wheeler's Fig. 10 or 16. 



2 This was figured by Lacaze Duthiers ('57 ) nearly fifty years ago. 



