In an earlier study (Yajima, 1960) of centrifugation of the egg of Chironomus dorsalis, the author obtained various types of double malformation (double cephalon and double abdomen) which are correlated with the orientation of the egg at the time of centrifugation. As a result the author proposed (1) that the embryonic character of Chironomus was determined by two formative localities; one located in the anterior end of the egg and determining the cephalic structures, and the other located in the posterior end and having a tendency toward abdominal development, (2) that the thoracic structures are determined as the result of interaction between the two localities and, finally, (3) that such localities must be carried by a substratum not moved by centrifugal forces of less than 27,000 g.

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