2IO A. RICHARDS AND DOXNELL J. GOOD. 



is that of some other forms, but the more important features 

 are described by a number of writers. Morgan, Jordan, Morris 

 and others in their descriptions of experiments have presented 

 normal conditions as well as results of experiments. 



In Cumingia eggs, Morgan ('10) found that normal develop- 

 ment may follow in eggs that have undergone very considerable 

 disturbances during experimental treatment, even "when the 

 visible substances are unequally distributed, and are carried 

 over into the blastomeres, redistribution being thereby pre- 

 vented." Cleavage is persistently normal under very abnormal 

 conditions, although very many factors may induce abnormal 

 development, and the results manifest themselves only later. 

 Abnormalities are especially apt to be caused by rough handling 

 of the eggs in sea water after laying, injury to the egg membranes 

 apparently being attended with serious consequences. "None 

 of the visible substances are essential to the development of 

 special parts of the embryo." 



Polyspermy occurs in Cumingia eggs generally unless the sperm 

 suspension be diluted before fertilization. This commonly is the 

 cause of abnormal embryos, if it is permitted to take place to 

 any extent at all. In our experiment the number of extra sperm, 

 while not large, varied definitely depending upon the dosage of 

 the X-rays, and therefore served a useful purpose in giving 

 additional information as to the effectiveness of the rays. 



The breeding season of Cumingia is at its height late in June 

 and during the month of July. In August it declines and fewer 

 eggs are laid by each female. The general impression prevails 

 also among those who have worked with this form most that at 

 the end of the season the egg is more easily injured, for instance 

 by physical treatment, and so the percentage of eggs of a given 

 lot which develops is less at that time. The number of eggs at 

 any time which will develop depends upon their manipulation, 

 for unnecessary handling with pipettes will cause low ratios. 



At the time of fertilization the egg is in the metaphase of the 

 first maturation division. Upon fertilization, maturation is 

 completed in the usual manner. 



The form and size of the first cleavage division is very constant 

 and definite. The first division is unequal, the CD cell being 



