34 BRIZZEE, JACOBS, KHARETCHKO AND SHARP 



TABLE I 



Comparison of Effects of Fetal X-irradiation at Various 

 Doses on Cortical Thickness 



Diflferences in brain weight (Fig. 6) between the 200 and 300 r series and 

 between these groups and the control animals were consistent and marked 

 throughout the four developmental stages studied. Brain weight in the 100 r 

 group, however, was higher in the 1- and 10-day animals and appreciably 

 lower in the 10- and 20-day stages than in the controls. At the 10- and 20- 

 day stages the differences in brain weight between all three radiated series 

 and between each of these groups and the nonirradiated rats were significant 

 at the .05 level or less. 



Results of behavioral studies are summarized in Tables II and III and in 

 Fig. 7. Table II shows the mean, variance, and number of rats for each of 

 the nine groups in the experiment on locomotor ability. The higher the 

 mean, the better the performance. From Table II it is clear that any initial 

 differences between the groups are overcome by 140 days. An analysis of 

 variance of these data, summarized in Table II, showed that the irradiation 

 (totaling 320 r) did result in a decrement of locomotor coordination on the 

 parallel bars for young rats. 



In the water maze experiment, 73 Cr of the control rats and 82 ^r- of the 

 half-body rats reached the criterion of one perfect trial by the twenty-first 

 trial, whereas only 26% of the full-body group did so (X" = 15.5, 2 df, 



