164 H. W. BEAMS. 



number of chromosomes. This type of maturation has been de- 

 scribed by Buchner in Astcrias, Lefever in Thalassema, Allyn in 

 Ch&topterus, Morris in Cumingia, and Brauer in natural parthe- 

 nogenesis of Artemia. These investigators report that apparently 

 normal larvae may develop from this type of maturation and the 

 embryos possess the diploid number of chromosomes. It appears 

 that normal development might follow this type of maturation in 

 Asterias when the chromatic and the achromatic figures appear 

 normal. The same chance of normal chromosome combination is 

 present as that which exists in fertilization, which is in harmony 

 with the conclusions of Boveri that normal development is depend- 

 ent on the normal combination of chromosomes. It would, 

 therefore, seem to be quite possible that another type of normal 

 development following artificial activation may take place in 

 Asterias which has a diploid number of chromosomes present. 



In few cases no polar bodies are extruded following artificial 

 activation. The first polar spindle may become directly the first 

 cleavage amphiaster or the first polar amphiaster may divide sub- 

 merged and form two nuclei which fuse to form ithe cleavage 

 nucleus. Tharaldsen states he has never observed normal de- 

 velopment following such abnormal conditions, which is probably 

 due to the abnormal chromosome combinations. 



In some cases the maturation monasters do not divide but pass 

 through definite cycles of activity involving the rhythmic disap- 

 pearance and reappearance of the rays and successive divisions of 

 the chromosomes without division of the aster or the cytosome. 

 Wilson ('01) has described five successive cycles of the monaster 

 which correspond to the two maturation divisions and the first 

 three cleavage divisions. In eccentric monaster eggs, at the telo- 

 phase of the cycle, the chromosomes collect at the focus of the 

 rays as the astral radiations disappear and give rise to a nucleus 

 with many chromosomes. Such eggs never cleave and activity 

 soon halts, followed by the degeneration of the monaster. 



The origin and nature of the central bodies in maturation are 

 similar to that described by King ('06) and Tharaldsen ('26) in 

 Asterias. The monaster of the first polar division appears " de 

 novo " just outside of the remnant of the germinal vesicle in the 

 cytoplasm. It divides to form an amphiaster which extrudes the 



