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Fish Moulds and Fly Moulds.—Several times has attention been directed in these pages to the mould which attacks fish in aquaria. This has been either as a query or a brief reply. The opportunity now occurs for making more extended observations on the subject. At page 10 appeared a communication on "A Dead Fly on the Window,"—this is significantly associated with the present question. The little mould therein referred to, called Empusina muscæ, is the terrestrial state of what seems to be an amphibious species, which in its aquatic condition has been named Saprolegnia ferax, and generally regarded as an Alga, but sometimes as a Fungus. It is not our intention to enter upon a dissertation as to its affinities and proper place in the vegetable kingdom; but our own opinion, strengthened by the recent investigations of Dr. De Bary and others on Fungi producing zoospores, certainly is in favour of regarding this mould and its allies as Fungi. If such a diseased fly as those described by W. M. B., in the paper already alluded to, are cast into water and allowed to remain, it soon developes a misty, filmy mouldiness around it, in a similar manner to the mould on fish in aquaria, and on the ova of fish, as well as upon molluscs and some other bodies, and just such a mould as that described and illustrated in the preceding page.

There are four genera known, each containing a greater or less number of species, and all bearing a great family likeness to each other, growing in water on similar substances, and doubtfully referred both to Algæ and Fungi. The name of Achyla prolifera cannot but be familiar to all who have paid any attention to disputed botanical questions.

A brief description of the development of one of these somewhat obscure vegetable productions must serve as a type of the rest. The first appearance presented by it is that of delicate threads, which are either simple or but slightly branched. These whitish threads radiate in all directions from the body whence they spring. The extremities of these threads become filled with granular matter, as figured on the other side (fig. 1), they gradually swell, and a division is formed across the thread, beneath the granular contents, which become rounded into little pellets (fig. 2). Each of these pellets separates from the rest, becomes an ovate spore which escapes by an opening at the top of the threads (fig. 3). These spores in Saprolegnia have two thread-like appendages, by means of which they move about in the water for a period as zoospores, until ultimately the motion ceases and germination commences. In Achyla prolifera the spores on insuing from the threads are at first enclosed in a membrane, which soon ruptures and sets the zoospores free.

A second form of fruit is also produced on other threads, lateral branches ending in globular sacs are formed, which contain resting spores (fig. 5), larger than the zoospores. Similar branches contain granular matter, which would appear to be antheridia, the function of which is to fertilize the resting spores (figs. 6, 7, 8). These large spores are called Oogonia. The walls of the globular sacs in which they are developed are perforated, so that through these perforations the resting spores are fertilized by the antheridia.

A third kind of fruit, described by Cienkowski, appears to have been observed also by J. S. T., in which a spherical sac, resembling those which contain the resting spores, is produced on a side branch, and contains spherical spores with a long tubular neck (fig. 9), which bore through the walls of the sac enclosing them and discharge minute swarming bodies into the water; these have not hitherto been known to germinate. Further information on this subject may be found in the "Micrographical Dictionary" under the head of Achyla, and also under Sporendonema.

Dr. Bingley, at a recent meeting of the Sheffield Field Naturalists' Society, gave a very interesting account of a wasp's nest which was exhibited. In April, 1864, he had tied some pieces of the Standard newspaper to a string, for the purpose of keeping the birds off some seeds he had sown in his garden at Whitley Hall. In May he observed a number of small holes in the paper, as if perforated by some insect. Watching it narrowly, he at length discovered a party of wasps at work upon it. By carefully following them, he traced them to an ivy bush, where he found them busily engaged building the nest exhibited, which he believed he was correct in stating to be constructed entirely out of the Standard newspaper. The animals appeared in the first instance to puncture a small hole in the paper, and then gather further supplies by gnawing round its edges, working it into pulp at the place, and after getting as much as they could carry, flying off with it to the nest. The comb was constructed simultaneously with the outer shell. The formation of the entire nest occupied until the middle of June, and the greater part of four whole newspapers were consumed in this manner before it was completed. To his surprise the nest was evacuated by them in the first week of August.

The solubility of granite in pure water and in hydrochloric acid are among the tests of its value. An indifferent granite was found to lose 0.25 per cent. of its weight in the former and 5 per cent. in the latter.—Ansted's Lectures on Practical Geology.