The American Monthly Microscopical Journal, Vol. 12
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| Stand: | 2015-08-04 03:50:33 |
Produktbeschreibung
Excerpt from The American Monthly Microscopical Journal, Vol. 12: Containing Contributions to Biology, for 1891 Nor do the valves separate along the raphé or median line, but along the line of junction or suture. If the reader will turn over a page or two to the conspectus, he will see it stated by H. L. Smith, of Tribe I, Raphidieæ, for example: "Frustules, mostly bacillar in s. v., always with a distinct raphe on one or both valves." (Italics mine.) Thus the two statements do not agree, and that on p. x will be likely to give the student a very different idea of what is meant by the raphe. But to return to our article. The trouble has all come, in my opinion, from calling the inner portion of the valve a hoop at all. For it suggests at once a barrel-hoop, something which is free at both edges from that which it encloses; which is not usually the case with the diatom hoop, to say the least. It is a misleading term, and is bound to confuse the student. It would be much better, therefore, it seems to me, to drop it altogether, or to speak of this piece as that portion of the membrane of each valve which when separated from the valve has the shape of a hoop. For as long as it is attached to the valve it is not a hoop, but the continuation of the valve itself. Finding this portion, however, at times detached, and shaped like a hoop, observers have thought there was only one hoop to each frustule, and that it bound the two valves together, whereas the truth is that there is a so-called hoop to each valve, and the hoops found in settlings of the Diatomaceæ did not come each from a frustule but each from a valve, that is, two from each frustule. (There may be a few exceptions, but in my opinion the above will hold as a general statement.) Now, I am inclined to believe that very few amateurs have had the occular demonstration of this fact. Having to write upon the subject, and finding it impossible to reconcile the figures with what Carpenter said, I went to my slides again, and with the binocular, and almost the first peep at Isthmia showed me that the drawings were faulty in representing the upper and lower edges of the two valves as continuous lines instead of broken ones. And then I took down Schmidt´s plates and the whole thing was as clear as day. And my advice to the student is to do the same thing: to pick out all his slides of Isthmia, Biddulphia, and Triceratium, and using the binocular, look sharp at the upper and lower edges of the hoop, and he will soon see that each is not one continuous line, but is formed by two lines, one of which is inside the other. And then if he is fortunate he will find some frustules where the valves have partly separated, and he will find that each valve has its band or hoop, and that it forms one continuous piece with the valve. And when he has done this he will have done something that is better than resolving Amphipleura, for he will have gained a definite idea of the structure of the diatom frustule. And this is a point that cannot be too strongly insisted upon, since even the Micrographic Dictionary has gone through edition after edition without stating or figuring the matter correctly. The first thing then for the student to do is to get a correct idea of the way the two valves are put together, and to do this he must not rely upon the figures in the Micrographic or in Carpenter, but study carefully the actual diatoms with the binocular. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com
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