GENERATION AND INHERITANCE 



305 



Fig. 9. 



DIAGRAM rv. Spermatogenesis, or development of the seminal bodies from the 

 seminal mother cells (spermatocytes) in Ascaris megalocephala bivalens. 



FIG. 1. Seminal mother cell with a nucleus (k) in which two tetrads (di) have 

 formed. Centrosome (c) with rays. 



FIG. 2. Seminal mother cell from the nucleus of which a spindle (sp) with two 

 tetrads has developed. Centrosome (c). 



FIG. 3. Spindle in which each tetrad has divided into paired chromosomes (dy- 

 ads). 



FIG. 4. The seminal mother cell is divided into daughter cells (tz) each of which 

 incloses a spindle with two pairs of chromosomes (dyads) (ch). The centrosome 

 (c) has divided into two daughter centrosomes between which a small new spindle 

 is formed. 



FIG. 5. The new spindle (sp) in each daughter cell has enlarged and included 

 the two pairs of chromosomes (ch 1 and ch j ). 



FIG. 6. In each spindle the pairs of chromosomes have separated from one 

 another and approached the poles of the spindle. 



FIG. 7. The two seminal daughter cells have divided into four granddaughter 

 cells (e2),each of which includes only two chromosomes (one element of the tetrad 

 of Fig. 1) and one centrosome. 



FIG. 8. The two chromosomes of the granddaughter cells (ez) have flattened 

 against each other eventually to form one small, compact, spherical nucleus (k). 



FIG. 9. Each granddaughter cell changes into a seminal body (sp) conical in 

 shape. Nucleus (k). 



