344 Thos. H. Montgomery. 



18. The Germ Cells. 



Assumed germ cells were (1) an uniisuallj large cell in the vicinity 

 of the anterior cumnlus at the late gastrulation, succeeded by (2) a 

 group of some eight large cells immediately bordering the gastrocoel, 

 which resemble at least in position the germ cells of the Scorpion as 

 described by Brauer (1894), and (3) discontinuous median masses 

 of small cells in the abdominal region before reversion. At reversion 

 no germ cells can be recognized with certainty. 



ISTone of the observers, Schimkewitsch, Kishinouye, Purcell, 

 Strand, who have described the germ glands and genital ducts distin- 

 guished germ cells until after the stage of reversion. 



19. Movement of Parts During Differentiation. 



The movements of the protoplasm during the course of development 

 are very prominent and full of interest from the mechanical side. 

 In the following lines I shall attempt to briefly analyze them. 



The ovarian egg has its cytoplasm in a delicate superficial layer 

 (blastema), and in a delicate intravitellar reticulum connecting this 

 with the cytoplasmic mass around the adcentral nucleus. Doubtless 

 there is some polarity of these parts, but I have not been able to 

 discover it. At maturation the nucleus becomes placed at the surface, 

 where it originates the first polar body; the second polar spindle then 

 moves centrad, forming the second polar body at the boundary of the 

 outer and inner yolk layers, and the egg nucleus (pronucleus) finally 

 reaches the center again (cf. my paper of 190 Y). These move- 

 ments are in all probability due to cytoplasmic currents. For it is 

 doubtful whether rounded nuclei or mitotic spindles possess automatic 

 movements ; they seem to be transported by the cytoplasm. And the 

 fluid yolk substance between the yolk globules is probably inert, as 

 are certainly the globules, and such flowings as it may exhibit are 

 probably induced by cytoplasmic influence. 



The cleavage of the egg consists of movements leading to the trans- 

 position of all nuclei and cytoplasm to the surface. This also is a 

 general cytoplasmic movement, of the nature of either a flowing or a 

 contraction. 



The later movements are in part upon the yolk surface; in part 



