STUDIES ONDALLASIA FRONTATASTOKES

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Abstract
D. frontata, a holotrichous ciliate (Chiliferidae), isolated and maintained in culture undergoes many changes in form. The ordinary tailed form may become navicular or boat-form and symmetrical, and then show marked changes in its reactions and movements. Such a form divides 4 times without intervening growth of the products until 16 minute cells are formed; sister cells of these 16 unite two-by-two within a capsule secreted by the cells and then fuse [long dash]a true paedogamous fertilization by copulation of gametes. The zygote eventually becomes a young Dallasia. Or the tailed form may not change into a navicular type, one means of preventing such change being the daily transfer to fresh medium, either flour-hay or cracked wheat. In mass cultures of tailed forms when the series is mature, epidemics of typical ciliate conjugation occur in the conjugation tests. Six series derived from such exconjugants are now maintained in isolation cultures. The significant feature in the life-history of Dallasia is the appearance of 2 types of fertilization[long dash]one by the fusion of paedogamous isomi-crogametes, the other by conjugation. The suggestion is made that endomixis in the ciliates generally is a reminiscence of an ancestral gamete brood.

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