ABSTRACT
Sea-urchin eggs generally develop quite normally after artificial fertilization. Sometimes it may be difficult to obtain good membrane elevation, but, after repeated washing in sea-water, fertilization and further development may be quite normal. In some batches of eggs abnormalities may, however, be observed in the pluteus stage, but these abnormalities, as a rule, do not change the pattern of the larvae profoundly. The defects are generally restricted to the arms and to the skeletal rods which, for example, may fail to grow out to their normal length, or may bend in an abnormal direction. Supernumerary rods may also appear, and rods may grow in an abnormal direction inside the larval body without causing a change in the exterior of the pluteus. During many years of experimental work with sea-urchin eggs, for the senior author dating thirty years back, we have never encountered, nor have we seen in the literature, examples of such an abnormal development as the one described in this paper.