The Modification of Developmental Patterns in the Sand Dollar with Maleic Acid

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Abstract
Continuous and short exposures of newly fertilized eggs of Dendraster excentricus to graded concns. of maleic acid cause inhibition of cleavage followed by inhibition of oral lobe, anal arms, and ventral surface. Occasionally, the ventrodorsal differential is completely obliterated. Differential conditioning to and recovery from the agent may result in the ventral area''s becoming increased and convex with anal arms at increased angles. Continuous and short exposures to the proper concn. of maleic acid, beginning at the mid-blastula stage, often result in a high % of radial plutei, as well as bilateral forms with flattened or convex ventral surfaces. Under the proper conditions a circle of arms, varying in number, develops around the base of the radial form, and the. enteron, while differentiating into 3 segments, does not develop the ventral bend. No exogastrulae appeared in these expts. following treatment with maleic acid. With high concns. and in certain lots of eggs, the apical regions became thickened, extended, and highly ciliated. Ventrodorsal and polar activity gradients are discussed, and the possibility of differences between these 2 fundamental patterns being related to enzyme correlates is mentioned.