PLATES 1 AND 2 



EXPLANATION OF FIGURES 



Figures to illustrate abnormalities produced by irradiation in early stages of 

 development. The specimens shown had apparently ceased development when 

 preserved. In each figure a view of the right lateral half of the specimen is shown 

 above, the median sagittal section below. In fig. 5 a dorsal view and a transverse 

 section through the posterior half of the body are also shown. 



1 to 10 Forms in which the vegetable pole of the egg is incompletely enclosed. 



I to 5 Cleavage cavity abnormally small or missing. 



1 Large yolk plug, archenteron fissure slight. 



2 Spina bifida; two slight tail buds; small archenteron; slight differentiation 



at an'ierior end of body. 



3 Spina bifida, tail bud partly developed; some differentiation of a heart; 



central nervous system solid mass of cells anteriorly, and bilaterally 

 divided posteriorly; archenteron fairly large. 



4 Hemi-embryo. Right half of egg undeveloped, left half partially devel- 



oped. 



5 Hemi-embryo. Left half well developed, right half only partially devel- 



oped, a, view of right side; h, view of back; c, median sagittal section; 

 d, transverse section through posterior part of body. 

 6 to 10 Cleavage cavity of normal size or abnormally large. 



6 Abnormally large cleavage cavity. No archenteron. 



7 Abnormally large cleavage cavity. Small archenteron; protruding yolk. 



8 Large archenteron; large cleavage cavity; solid central nervous system; 



protruding yolk. 



9 Similar to figure 8, but further differentiated. • 



10 Fairly normal differentiation except in vicinity of anus. 



II to 16 Forms in which the yolk has been enclosed by ectoderm. 



11 Abnormally large archenteron. No definite differentiation of a neural 



plate. 



12 Abnormal archenteron. Neural region a solid plate of cells without 



definite neural grove. 



13 Slight central cavity at anterior end of central nervous system but none 



posteriorly. 



14 Solid central nervous system. Small and abnormal archenteron. 



15 Fair differentiation but backward and distinctly abnormal. 



16 Abnormally dilated central canal of central nervous system and abnorm- 



ally dilated archenteron. 

 Figures illustrating abnormalities in larva; which reach a higher stage of devel- 

 opment than those described above have been published in The Journal of Exper- 

 imental Zoology, vol. 4, 1907. 



