THE occurrence of microspores in centric diatoms and their possible nature have been the objects of great discussion. Recently, Gross1, on the basis of cultures of Chaetoceros pseudocrinitus and Ch. didymus, concluded that “there is no evidence whatever that these microspore-like bodies found in the cultures of Ch. pseudocrinitus acted as reproductive cells. They were never liberated or at any rate never found outside the parental cells, and flagellate-like cells were never found in the cultures where their formation had taken place”. He tentatively put forward the view that “what have been described as microspores are either abnormal products of the diatom cell or alien flagellates, neither participating in the life cycle of the diatoms”.