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 not familiar by reference to our sketch. (Plate II., Fig. 7] Two individuals approach one another, and a communication being established between them through the bases of their separated halves, the cell-contents are poured out into the intervening space and there form a spore, generally spherical and at first smooth, but in the mature state often ornamented with tubercles or spines. In this condition the structure and markings of the empty cellulose cases are beautifully displayed.

What is the exact series of changes by which the original form is developed from the spore requires further investigation, in spite of Berkeley's statement that it is propagated in some species by division, exactly after the fashion of the ordinary cells, and in the third generation acquires its normal form.

Other points in the physiology of these plants also await further research, as, for instance, the nature of the curious circular hyaline spaces filled with moving granules, which are seen in the ends of the frustules of Closterium and Penium; the circulation of similar particles between the cell-walls and the endochrome; and the remarkable "swarming" of the entire cell-contents, which occurs in some genera, probably before conjugation, when every grain of endochrome seems to be rushing wildly in and out among its fellows in a sort of giddy dance.

Passing from the unicellular to the filamentous Algæ, which consist for the most part of elongated cylindrical cells placed in juxtaposition, and to end, in various arrangements, we are compelled by want of space only to glance at many large and interesting orders. Among these are the Batrachospermeæ, represented by the exquisitely graceful genus Batrachospermum, whose gelatinous tresses of tender grey or olive green whorled branchlets are not uncommon in clear streams in this district; the almost equally beautiful Chætaphoraceæ, of which abundant examples are to be found in the deep green gelatinous masses of Chætophora endiciæfolia and C. elegans, in the tender preen filaments of Draparnaldia plumosa waving gracefully in clear running waters, and in the singular disk-shaped fronds of Coleochæte scutata, found adherent lo leaves of submerged aquatic plants; the Oscillatoriaceæ, which comprise many singular forms, inhabitants of pools, wet rocks, damp ground, &e., and well represented in our district; and finally the Nostochaceæ, of which the typical genus Nostoe contains many species, consisting of long beaded filaments. twisted like intricate coils of rope, and agglomerated into gelatinous fronds ranging in size from that of a pea to that of a walnut, most cosmopolitan in their habitats. rejoicing in situations so various as clear streams, exposed moorlands, and thatched roofs.

In what remains of this paper we purpose to refer in some detail to three of the remaining groups of Confervoid Algæ, each of which presents interesting points of structure and remarkable aspects of the phenomena of reproduction.

First among those is the large family of Siphovaceæ, of which the commonest examples are the various species of Vaucheria, some of which