Bibliographical Notices, 349 the reproduction of those Freshwater Algae in which zoospores form the commonest means of propagation. From the recogni-tion of the contemporaneous existence of zoospores or gonidia with sexual organs of reproduction in Vaucheria, he is led to conjecture the existence of a similar condition in other genera. In Achlytty both zoospores and resting spores are known, and he suspects that the slender branches found upon those filaments of Achlya which bear sporanges, will prove to be antheridia. In (Edogonium, the membrane of the sporangial-cell bursts before the formation of the spore-coat, which admits of the possibility of a penetration of spermatozoids. In BulbochatCj a fissure is also met with. Now in these genera, besides resting-spores and ordinary zoospores, we find exceedingly small bodies, resembling the zoospores in their structure, called by A. Braun microgonidia. These are developed in cells smaller, and differ-ing in character from the ordinary vegetative cells. They germinate, but produce small bodies, composed only of one or two cells, which, it is remarkable, are always found attached upon the sporangia, or near them. Here they dehisce and discharge their contents. Although no trace of spermatozoids has been perceived in them, this discharge of the contents near the opening of the sporangial membrane tends to the conjecture that they exercise an impregnating influence on the resting-spore. If this be the case, we should have the curious phse-nomenon of the male structure being developed as a special separate body, a kind of prothallium. With the above peculi-arities is associated in Bulbochate a curious mode of germination of the resting-spores. Examples of these kept through the winter produced, not a new filament, but four ciliated zoospores, which escaped, came to rest, germinated, and then produced new filaments. A similar phsenomenon was observed in the case of the resting-spores of Coleochate, The paper concludes by a summing up of the results, which will be unnecessary after this brief abstract. BIBLIOGRAPHICAL NOTICES. A History of the British Marine Testaceous Mollusca, distributed in their Natural Order. By William Clark. London : Van Voorst, 1855. The study of malacology, or of the true natural history of the Mollusca, has sprung up almost entirely within the last half-century. Up to this period the attention of zoologists in this department was almost exclusively directed to the shells of these animals, the only part which admits of being easily preserved in the cabinet or trans-ported from a distance, and the structure of the creatures producing
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