CROSS- AND SELF-FERTILIZATION IN THE ASCIDIAN MOLGULA MANHATTENSIS

¹ From the William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, California

Tests of self- and cross-fertilizations of the single ascidian Molgula manhattensis, were made during August and September, 1941, at Woods Hole. It was found that 100 per cent self-fertilization occurred in less than half the cases (see Table I), but in others the percentages ranged from 1 to 90 per cent. One hundred per cent of cross-fertilization occurred in practically all cases. The occurrence of normal and abnormal development was observed, and many cases of abnormal embryos as well as normal tadpoles were found, but, owing to the fact that many embryos metamorphosed directly, or at least without passing through a free-swimming tadpole stage, the numerical results are not reported here. A closer set of observations are needed to give reliable data as to whether self-fertilized eggs give rise to such development more often than do cross-fertilized eggs. Two mature individuals were found that had only ovaries. Their eggs gave 100 per cent cross-fertilization.