Though the attention of several physiologists has been directed to the Tubularian Zoophytes, and though the elucidation of many points of interest in their structure and in the physiological phenomena presented by them has been the result, yet in numerous most important particulars our knowledge of the Tubulariadæ is still very imperfect, notwithstanding the great value which a more thorough acquaintance with these simple organisms must possess in its bearing upon some of the leading questions in physiology. It was with the view of filling up some of the deficiencies which still exist in our knowledge of the lower zoophytes, that the following researches were under taken; and Cordylophora lacustris , affording as it does a fine typical example of tubularian structure, and being easily kept alive for months, was deemed peculiarly favourable for prolonged and careful observation; the results, moreover, which have been obtained from the investigation of this zoophyte, have been in many instances confirmed and extended by corresponding inquiries, instituted at the same time into the structure of allied genera.