Cortical morphogenesis in Paramecium aurelia following amputation of the anterior region

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Abstract
The most anterior approximately 35 μ of the 49–50 μ long anterior region was removed from many paramecia by a transverse cut. The challenge imposed by the amputation met with the following responses in lines of successive proters (anterior products of fission). Restitution of the anterior region in successive proters. Most of the restitution occurred at the first fission which yielded proters having anterior region about 55% (as compared with the approximately 30% remaining after amputation) and posterior regions 68% of normal length. Return to normal was nearly complete after the eighth fission. Incomplete kineties in successive proters. The anterior termini of incomplete kineties came to be located more and more posteriorly in the course of successive fissions as growth occurred anterior to them. When the anterior termini came to be posterior to the fission plane, they were lost from the proters formed at this and subsequent fissions. Proters with reduced kineties were slenderer than normal. Dorsal kinety pattern in the proters. On the dorsal field, after all short kineties were lost from the proters, the remaining kineties were normally oriented anterior‐posteriorly. However, the normal arrangement of the anterior termini of kineties at the suture, on the dorsal anterior tip of the proters, was lacking. Ventral kinety pattern in the regenerated anterior region. Regenerated anterior regions possessed normal or nearly normal ventral kinety patterns. Deviations from normal were minor. The preoral suture. Normally this is a clear space at the juncture between the anterior ventral right and left field. The regenerated part of the suture was atypical: the clear space was lacking. Inheritance and variation of total number of kineties around the cell. In a slender clone, the mean number of kineties was 67 as compared with 75 in an uncut control clone. The difference was inherited for many fissions, but not permanently. Normally, the number of kineties decreases slowly when fission rate is low due to limitation of food and rises slowly when excess food is supplied. Abnormal buccal structures. Cuts made close to the vestibule, but not those further from the vestibule, resulted in death or in abnormal clones with defective buccal structures of various sorts.