Turbellarian taxonomic database

Record # 19015
Sonneborn TM (1930)
Genetic studies on Stenostomum incaudatum (nov. spec.). I. The nature and origin of differences among individuals formed during vegetative reproduction.
J. Exp. Zool. 57: 57-108.

Abstract / Notes

In studies on S. incaudatum, source unknown but probably eastern U. S. A., it was found that lead acetate had
different effects on the anterior and posterior products of division. The present paper deals with the
grounds for this difference. Series of only anterior products of division went through a continuous process
of development, finally decreasing in rate of division, degenerating in structure, and dying. Such a series,
therefore, has the characteristics of a single individual producing offspring from its posterior end. These
posterior products of division have the characteristics of young, newly-formed individuals. A series of only
posterior products of division ordinarily do.es not show continuity of development, decrease in rate of
division, degeneration in structure, or death. Such a series is "potentially immortal." Among individuals
(i.e., series of only anteriors) of a clone, there were 11 types differing in structure, development and
length of life. Ten of these types[long dash]including, however, only 3% of the individuals produced[long
dash]are derived only from parents undergoing structural degeneration. Within each type there is variation in
the number, position, form and nature of the structures characteristic of advanced age, and in the sequence
of the stages of degeneration. Differences in the structural endowment of the 11 types of individuals are
determined not merely by the age, but also by the structural condition of the parent. Some of the structures
arising with age are at times transferred from parent to offspring. Differences in later development depend
partly on the extent to which this occurs. Differences in length of life depend chiefly on differences in
original structural endowment and on differences in the course these structures follow during development.
Knowledge of these differences among individuals of a clone is important in understanding the effects of
environmental conditions.

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