74 J- F. McCLENDON. 



plasm, as copulation is necessary to long continued existence of 

 Paramcecia. It is probably chiefly thus that the heritable quali- 

 ties residing in the chromosomes are conveyed to the cytoplasm. 

 I do not mean to say that this is the only way the nucleus affects 

 the cytoplasm, for with a few exceptions (7. e., red blood cor- 

 puscles of higher animals) cytoplasm not containing a nucleus 

 soon dies, but if the heritable qualities are stored up in the chro- 

 matin, part of this chromatin bearing these qualities could be 

 transferred to the cytoplasm more easily during the absence of a 

 nuclear membrane. 



After the close of the fifth cleavage (32 cells) the embryo is 

 composed of three types of cells that differ visibly. 



1. The primary germ cell. 



2. The primary entoblast cell. 



3. Thirty cells of the blastoderm all similar in appearance. 

 The primary germ cell when first separated from the entoderm 



looks like the other cells of the blastoderm, but during the rest 

 grows larger than its neighbors and is delayed in mitosis. In 

 this character of delayed mitosis it resembles its sister cell (pri- 

 mary entoderm cell). There is nothing characteristic of its posi- 

 tion that could cause it to become different from its neighbors, 

 so we must ascribe this difference to the difference in the sub- 

 stances entering into it which in turn may be caused by unequal 



cleavage. 



VII. SUMMARY. 



i. My observations on the cell lineage agree in general 

 with those of Pedaschenko (who worked it out to the 16 cell 

 stage) save in regard to the orientation. Pedaschenko used no 

 means to distinguish between the two flat sides of the egg and 

 was mistaken in regard to the location of the animal pole, as I 

 have shown <p. 50). At the fifth cleavage the yolk cell buds 

 off the last protoplasmic cell, which is the primary germ cell. 

 After extrusion of the germ cell (32 cell stage) the yolk cell is 

 purely entoblastic. The segregation of the entoblast takes place 

 one generation later than in Lcpas (Biglow '02), and the segrega- 

 tion of the germ cells one generation later than in Cyclops 

 (Haecker). The delay in the segregation of these two elements 

 is probably due to the large amount of yolk present and the 

 compressed condition of the egg, which cause delay in gastrula- 



