THE EFFECTS OF HYDROSTATIC PRESSURE UPON THE POLAR LOBE AND CLEAVAGE PATTERN IN THE CHAETOPTERUS EGG

¹ From the Marine Biological Laboratory, Woods Hole, Mass., and the Physiological Laboratory, Princeton University

1. The polar lobe of the Chaetopterus egg is withdrawn and the cell rounds up under a hydrostatic pressure of 220 atmospheres if the pressure is applied in the early stages of lobe formation. A pressure of 270 atmospheres is necessary if the cleavage furrow is deeply cut.

2. This phenomenon is interpreted as due to the liquefaction of the cortical gel which gives the polar lobe its structure. Further evidence is added which leads to the belief that polar lobe formation is primarily a cortical effect of the vegetative pole region, to a very large degree independent of the underlying cytoplasm or the mitotic apparatus.

3. The suppression of the polar lobe and the cleavage furrow by pressure is partly reversible in that they re-form for the succeeding cleavages, but pronounced abnormalities in the cleavage pattern are characteristic. Typical irregularities are considered, including examples in which the first or second cleavage furrows have been produced equatorially.