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THE AMPHIBIAN GERMINAL VESICLE 



Half or medium-sized egg vesicle (nucleus) 



1. Nuclear sacs small. 



2. Nucleoli are next to nuclear wall. 



3. Chromosome frame fills the entire nucleus. 



4. Chromosomes are spread out to their maximum extension, and possess 

 large lateral loops. 



Small-sized egg vesicle (nucleus) 



1. Nuclear sacs barely visible. 



2. Nucleoli peripheral. 



3. Chromosome frame fills the entire nucleus. 



4. Chromosomes are much smaller than in the larger nuclei. 



Normal nuclear growth cycle of the ovum of Rano pipiens. (Stage 1) Smallest 

 follicle in which the chromosomes within the germinal vesicle con be seen. 

 (Stage 2) The paired chromosomes are barely visible, embedded in a nucleo- 

 plasmic gel. Egg diameters less than 200 microns. (Stage 3) Eggs measuring 

 from 200 to 500 microns in diameter, more detail visible through the trans- 

 parent theca cells. Lateral loop production begins. Zone of large irregular 

 nucleoli may be seen just beneath the nuclear membrane. (Stage 4) First 

 development of yellow -brown color and yolk. Eggs range in size from SCO to 

 700 microns in diameter. Chromosomes attain length of about 450 microns. 

 For salamanders of comparable stage chromosomes measure 700 microns in 

 length. (Stage 5) Chromosome frame begins contraction while the nucleus 

 continues to grow in eggs ranging in diameter from 750 to 850 microns. This 

 is approximately half the ultimate size. Chromosomes shorten and have fewer 

 and smaller loops. The major nucleolar production continues and sacs appear 

 on the surface of the nuclear membrane. (Stage 6) Egg diameter about 1. 8 

 millimeters and germinal vesicle is of maximum size. Chromosome frame 

 now about 1/1000 of the nuclear volume, coated by a denser substance which 

 can be coagulated by the calcium ion. Chromosomes have shortened to 40 

 microns or less and have lost all large and small hyaline bodies called loop 

 fragments. 



Heavy arrows indicate the mixing of nuclear material in the cytoplasm after 

 the breakdown of the germinal vesicle. The dotted arrow indicates migra- 

 tion of the central chromosomal mass toward the animal pole to become the 

 maturation spindle for the first polar body. (From W. R. Duryee, 1950, 

 Ann. N.Y. Acad. Sci. , SO, Art. 8.) 



