458 MARIE A. IIIXRICHS. 



in the formation of the zygote nucleus nor in subsequent cleavage 

 figures. Packard, '18, found that radiation of the egg of Chas- 

 /0/>/m<s before fertilization prevents the egg nucleus from taking 

 part in division, although the sperm nucleus behaves normally. 

 Richards and Good, '19, found that radiation of Cumingia 

 sperm did not affect the rate of cleavage, and that radiation of 

 fertilized eggs produced first an acceleration in the rate of 

 cleavage followed by a retardation. On the other hand, brief 

 radiation of the unfertilized egg produced retarded cleavage and 

 abnormal development. Exposure of sperm was less effective 

 than exposure of unfertilized eggs. Redfield and Bright, '21, 

 have shown that exposure of Nereis eggs to ultraviolet radiation 

 interferes with the production of normal membranes. 



In some of the above-cited work where the later development 

 was observed, it is interesting to note that the departure from 

 normal development appeared in systems and organs which are 

 known to have a high rate of physiological activity. Similar 

 conditions are found when either or both of the germ cells of 

 Arbacia are exposed to ultraviolet radiation, or to visible radi- 

 ation following sensitization. The region of the egg which is 

 destined to give rise to the oral lobe and the anterior end of the 

 pluteus has its normal development modified to a greater degree 

 than the other parts of the egg. The resulting embryos show 

 greater inhibition or even absence of development of the oral 

 lobe and aboral arms. 



Method. As in previous work, two regions of the spectrum 

 were used, the ultraviolet region, and the visible region following 

 sensitization. 



Ultraviolet Radiation was obtained from a quartz Hg-vapor arc 

 (Cooper Hewitt), running at 60 volts, 4.0 amps. The experi- 

 mental material, in open dishes, was placed approximately 30 cm. 

 below the center of the arc. The above source is rich in ultra- 

 violet radiation, although its spectrum extends well into the 

 visible region (1,850-7,700 A.). 



Visible Radiation. In this group of experiments, eggs or 

 sperm were exposed in weak concentrations of dyes (1/2,000- 

 1/20,000), to radiation from one of the following light sources; 



i . A i ,5oo-watt Tungsten filament lamp burning tip-down at a 



