ACTION OF VISIBLE RAYS ON ARBACIA EGGS. 5 



transitory, wide-angled forms, some up to 180, with over- 

 developed oral lobes give evidence that the median anterior 

 region has recovered from a slight inhibition and that its rate of 

 growth has surpassed that of other regions (Figs. 23-27). 



C. General Recovery. Individual differences in eggs from the 

 same female (see also Medes, '17, and Tennent, '10) produce 

 differences in degree, and even in direction of effect; but the 

 larger number (90 per cent, or more) of the embryos in a given 

 lot may, for example, show differential inhibition, while the rest 

 of the embryos in the lot may show general recovery or no effect 

 at all. The degree of effect produced is roughly proportional to 

 the dosage (see Figs. 58, 63) and is also greater at higher tempera- 

 tures. (See Bovie and Daland, '23, Bovie, .'18.) 



D. Differential Acclimation. Differential acclimation results 

 when the inhibitory effect of radiation is mild enough to permit 

 adjustment, for example, when the eggs are exposed continuously, 

 in weak concentrations of dyes, to diffuse daylight, or are kept in 

 stronger concentrations for several days in the dark. The 

 resulting forms, are wide-angled and have over-developed oral 

 lobes like those appearing after differential recovery. (See 



Figs. 37-39-) 



In higher concentrations there is a differential effect on develop- 

 ment even in the dark (Figs. 33-39) ; but in order that the lower 

 concentrations may be effective, there must have been at some 

 time, preferably during early development, an exposure of suf- 

 ficient duration to radiation of the proper intensity. The effects 

 produced under these conditions can to some extent be controlled. 



Frequently there appears a larger number of aboral arms than 

 normal (Figs. 40-41). Probably these result from the activity of 

 mesenchyme cells which under normal conditions are inhibited in 

 development. (Child, 'i6a.) (The possibility of stimulation of 

 calcium metabolism by radiation should also be considered.) 



Long exposures to radiation (7 minutes under Tungsten bulb, 

 or 90 minutes in sunlight) produce some differential inhibition in 

 unstained eggs (Figs. 42-47). In our previous work with activa- 

 tion of Echinoderm eggs by photodynamic action it was found 

 that strong illumination frequently induces membrane formation, 

 especially in eggs having more than the usual quantity of pigment, 

 echinochrome. (Lillie and Hinrichs, '23.) 



