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Show 648 MR. R. J. LECHMERE GUPPY ON SOME [Nov. 6, that " they exhibit an early condition of Polymorphina, in which we see an entosolenia, slightly modified, playing the part of the primordial chamber of this form. This entosolenian condition of Polymorphina is nearly always apparent in specimens sufficiently small or unadvanced to leave the early chambers translucent and open to examination As they advance in growth the individual Polymorphince are invested with additional chambers after a type peculiar to themselves, but in a very irregular manner as regards the capacity and shape of the chambers." If such a unicellular Polymorphina as the one shown in my fig. 7, or in Parker and Jones's figure just referred to, takes on additional chambers in a regular series on one side only instead of alternately on different faces of the shell, it becomes a Cristellaria either straight, curved, or involute. In further explanation it may be stated that in Polymorphina the chambers are developed alongside of, and adherent to, each other and the primordial chamber like drops of resin which have exuded from a tree. But if the chambers are developed in a single symmetrical and regular series, straight or curved, each segment being developed from and adherent to the preceding one only, the organism is a Cristellaria, and so may attain a considerable development in this shape. The Cristellarian segments are added consecutively on one side only of the previous segment, and may be represented as one of the branches of a letter V inverted, the aperture being at the one end (the apex) of the V ; the other branch, in the case of a true Cristellaria, not being developed. If, however, at a certain stage, the other branch of the V becomes developed, the previous segment being embraced, not on one side only, as in the Cristellarian form, but on both sides, and the aperture being at the apex, we have a Flabelline Frondicularia. In this form, generally speaking, the segments are extremely compressed, the whole test being scarcely as thick as ordinary paper. In fig. 1 (Plate XLI.) we have a shell with a Cristellarian beginning, passing into a Nodosaria. This may be called the Amphycoryne-ibrm of Nodosaria, just as tbe specimen delineated in fig. 3 may be called the Flabellina-iorm of Frondicularia. The specimens figured illustrate the development of the genera to which we give the names of Frondicidaria and Nodosaria, and suggest the conclusion that the primordial forms from which they were evolved resembled a Lagena and that the next steps of the evolution were represented by Polymorphina and Cristellaria. Frondicularia is no doubt the next step in one direction ; whilst in another the evolution takes the line of Nodosaria. Hence it appears that Nodosaria is not directly developed from Lagena. The generic forms called Polymorphina, Uvigerina, and Sagrina intervene. W e have thus an explanation of facts hitherto not quite easily explicable, namely, for example, the development of many Foraminifera from a more complex (biserial, triserial) form to a simpler (uniserial) form. In most individuals belonging to genera such as Frondicularia and others of the Nodosarian series |
