The peculiar capsule-openings of the PHÆODARIA were first discovered and carefully described by Hertwig in 1879 (L. N. 33, pp. 95, 107). He found in all the six genera which he examined _three_ openings, a main-opening at the basal pole of the main axis and two accessory openings, one on either side of the apical pole; hence he named the whole group "TRIPYLEA." This name, however, is not applicable to the numerous PHÆODARIA mentioned above, which have only a main opening without any accessory openings, nor to those genera in which the number of the latter is variable. I have, therefore, replaced Hertwig's designation by the term "CANNOPYLEA," which has reference to the peculiar tubular form of the opening. This I find much more developed in many PHÆODARIA than Hertwig has represented, and I must also, in certain particulars, dissent from his delineation of the minute structure, although this is in the main remarkably accurate.
61. _The Nucleus._--The nucleus, enclosed in the central capsule of all Radiolaria, behaves in every respect like a true cell-nucleus, and thus lies at the base of the now universal opinion, that the whole Radiolarian organism, in spite of its varied development and remarkable variations, is unicellular and remains throughout life a true individual cell. This important theory is not invalidated by the fact that the nucleus undergoes peculiar modifications in many groups, and in certain groups presents appearances seldom or never seen elsewhere.
62. _Uninuclear and Multinuclear Radiolaria (Monocaryotic and Polycaryotic)._--All Radiolaria present two different conditions in respect of the behaviour of the nucleus, since in their young stages they are uninuclear (_monocaryotic_), and in later stages multinuclear (_polycaryotic_). This is readily explained by the fact that each individual Radiolarian is developed from a simple unicellular swarm-spore, and that afterwards, before the formation of swarm-spores, the single nucleus divides into many small nuclei. Thus in the Radiolaria the nucleus is pre-eminently the _organ of reproduction and inheritance_. The division of the originally single nucleus into many small nuclei may take place, however, at very different periods, so that the Radiolaria may be divided in this respect into precocious and serotinous.