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Asexual Reproduction in Acoelous Turbellaria †

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Department of Zoology, Yale University ASEXUAL REPRODUCTION IN ACOELOUS TURBELLARIAt Among the turbellarian flatworms reproduction is typically associated with a sexual process. However, in certain orders such as the Tricladida and Rhabdocoela asexual reproduction is also recognized.8 The purpose of this short paper is to report the discovery of asexual reproduction by what is probably a fission-like process in another order of Turbellaria, the Acoela. Asexual reproduction was discovered in immature forms of an acoel worm identifiable as Amphiscolops langerhansi (Graff) except for the fact that it lacked the statocyst typically present in this species. However, absence of the statocyst can be explained as a consequence of asexual repro- duction. This will be made clear after the data in support of asexual repro- duction have been presented and these data comprise both indirect evidence as well as direct evidence. During the course of culturing immature A. langerhansi (worms 2-3 mm. in length, no visible sexual organs) there appeared in the cultures, quite consistently, small odd-shaped worms (Fig. 1). These forms, though mark- edly different from the larger worms in the culture relative to size and external morphology, did seem to be some form of A. langerhansi: first, because their pigmentation (concrement granules and symbiotic algae) and bilobed posteriors closely resembled the same characters in the larger worms; second, because these were pure cultures and there was no possible source of other flatworms. Such forms were occasionally seen in the aquaria, but were hard to find because of their small size. To determine whether or not these small worms appeared in cultures containing only one of the larger worms, five of the immature worms were isolated into separate culture depressions. Observations were made daily for varying lengths of time and the new, odd-shaped worms removed as they appeared. The overall data are as follows: Odd-shaped little worms appeared in each of the culture depr

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