28 ; formation of first five radial pouches, 28 j formation of succeeding radial pouches, 28 ; relation of stalk of preoral coelom to hydroccele ring, 29 j relation of pouch I to posterior cmlom, 29 ; the dorsalsac, 29 ; axial part of anterior coelom, 29 ; internal oral circular sinus, 30 ; axial organ, 30 ; stone-canal, 31 ; relation of madreporic pores to stone-canal and axial sinus, 31 ; pouch IX/I of external oral circular sinus, 31.25 25.
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James F. Gemmill (1912) studied this question.