« AnteriorContinuar »
Synura. The differences in the results just referred to arise mainly from corresponding differences in the direction of the cleavage in the successive fissions. In Volvox, we have the first cleavage into two protoplasms, taking place vertically to the surface of the parent sphere. The second also takes place vertically, but in a direction at right angles to the first. The next division appears to take place along a plane parallel to the surface of the parent sphere. Hence, as soon as we obtain eight distinct protoplasms, we find them arranged in two parallel layers, the thin space between the two representing what is ultimately destined to become the hollow interior of the young sphere. In Spharosira, on the other hand, though the fissions change their direction, they result in the formation of a disk, and not in a double series of protoplasms, because they are all made vertically to the surface; the horizontal ones of the ordinary Volvox not taking place. When Mr. Carter pursued his observations on the subject, he thought he had found examples in which each disk consisted of 128 ciliated segments. If this is true, and I see no reason for doubting it, segmentation in his case had been repeated seven times, whilst in mine they were limited to five. In both instances the process was completed, since, in both, the separate protoplasms became provided with cilia—a stage of growth which, so far as my experience enables me to judge, always indicates the completion of the segmentative process, and the final determination of the number of gonidia into which the mass is destined to be divided. The young organism now assumes a new character. Hitherto it has been passing through a stage of still life; it is now furnished with locomotive organs. If we examine carefully one of the disks in this completed stage, we shall find that it exhibits appearances represented in figures 6 and 7. In the former, we have a flat disk consisting of thirty-two green protoplasms, looking somewhat like some forms of the genus Pediastrum. Fringing this disk, we can trace a number of freely moving cilia (6, e). Each protoplasm, in this respect, resembles the parent gonidium (fig. 2) from which it originated; but as we watch, we observe that the disk rotates slowly; in one instance I was able distinctly to trace the walls of the mother-cell (7, d) within which it was imprisoned. In this movement of the disk within the interior of the mother-cell we have another feature of affinity with Volvox-in which latter, as I long ago pointed out, a similar movement of the young imprisoned sphere may occasionally be observed. In the Sphærosira this revolving motion affords us facilities for observing the lateral aspect of the compound disk, and of the individual protoplasms composing it. We now see that each of the latter is elongated, and slightly curved. The centre of
the upper surface of the compound disk (fig. 7, a) appears to be a little depressed. The lateral concavity of the curved protoplasms (7, b) is in all cases directed inwards. Throughout the greater part of its length each protoplasm exhibits the same green colour and numerous bright granules that appear in its upper surface; but its lower extremity (fig. 7, c), which before movements began was directed towards the centre of the parent sphere, is colourless; and from it is projected apparently a single cilium (7, e). From their rapid motion I found it impossible to count them; and even when aided by tincture of iodine and other reagents the result was equally a failure; but my impression was, and is, that each protoplasm bore a single cilium, not two. In this stage of its development, each protoplasm bears the closest possible resemblance to an Euglena—the motile condition of Protococcus pluvialis. I am convinced, that if one of the gemmæ of Sphærosira and an individual Euglena viridis were placed side by side, they would be wholly undistinguishable. By what means the several protoplasms were bound together I was unable to ascertain. Neither did I succeed in tracing their ultimate condition after the Volvocinæ as a whole disappeared from the jar. As already observed, when they began to do so, they vanished rapidly, and nothing was left in the water indicative of the myriads which it contained a few days before but numerous spores, if such they are, of Volvox aureus. When I found that this was the case, I visited the pond whence the specimens were obtained on May 26. Not one solitary example could be found either of Volvox or of Sphærosira; neither could I discover a trace of Uvella, or of any of its compound allies which could be identified as having been developed out of a Sphærosira. A few examples of Euglena longicauda were the only moving forms of protoplasm that presented themselves. I then turned my attention to the mud at the bottom of the pond, collecting its surface-layer by means of a glass tube. Spores of Volvox aureus in various conditions were not unfrequent, but nothing like the young compound gemmæ of Sphærosira were to be seen. There was every reason to conclude that the latter were as temporary and fugitive in their nature as the young spherical gemmæ of the common Volvox, and, like them, had wholly passed away. What then are the compound gemmæ of Sphærosira?
Mr. Carter believes them to be a spermatic form of Volvox, each separate Euglenæform organism being a true spermatozoid. I confess I see no reason for accepting this determination. I have been unable to detect in these objects any evidence of sexuality, and am more disposed to conclude, with Professor Busk, that Sphærosira is merely a Volvox in which
the development takes place in a peculiar way. The peculiarity is twofold. First, instead of some half-dozen of the gonidia being selected for fission and development into spheres, as in Volvox, in Sphærosira fully one-half of the entire number contained in the organism are developed. Then there is, secondly, a difference in the direction of fission. In Volvox, as already seen, this fission not only takes place along various planes vertical to the surface, but also in others that are horizontal to and parallel with it. In the Sphærosira we have the former system of cleavages, but not the latter. Hence the separate protoplasms are grouped in a single plane with their long axes vertical to the surface of the tabular disk. This limitation of the direction of cleavage thus reduces itself to a comparatively small matter, and appears to me not only to indicate no generic distinction, but not even a specific one. It merely exhibits one of the incidental variations in growth and development so common amongst these lower algæ, and, regarded physiologically, has no special value; least of all does it appear to bear any relation to the sexual reproductive processes so common amongst the higher cryptogamia.
TN amateur musical work, either for home use or for trainI ing a choir, difficulties are often found about the different keys in music, their signatures, and rules for transposing pieces up or down, as may be needed for suiting various voices.
Now some most useful helps may be got on these points by an examination of the musical interval of the fifth, from which by a little cross-questioning we may draw some rules for popular use which are not generally found in musical treatises. These, in general, give directions without explanations of their modus operandi.
We therefore propose to make the interval of the fifth in music perform a little “musical magic,” and tell us these points:
1. In what order different keys follow each other.
2. What notes are to be made sharp or flat in the signatures, and in what order they follow each other.
3. How to know by inspection what keys pieces are written in, and into what they may be transposed.
4. What changes have to be made in the signatures of keys to transpose pieces up or down, any number of notes.
II. We must first, for the sake of clearness, recall to mind a few definitions of musical terms necessary for our purpose.
The ear teaches us that a certain sequence of notes rising up from the starting note or key note, such as C, must follow each other in a certain regular course, if a pleasant effect is to be made, and this succession of notes is called the major scale of that note. It comprises eight notes, the last being the octave above the key note. It is found on examination that the interval between these notes are as follows:—First, 2 whole tones, then I semitone; next, 3 more whole tones and 1 more semitone: or to put it in a series of letters, marking the semi
tones with a circumflex, we get this order for a major scale of
C, D, E, F, G, A, B, C, .
1, 2, 3, 4, 5, 6, 7, 8; where the semitones must occur between the 3rd and 4th, and between the 7th and 8th, notes of the scale. This is the case for any of the other notes, if made the starting or key note of a piece of music. But in the case of any other key note except C the semitones will therefore need rearranging, which is done by adding sharps or flats to the notes of the scale until the right succession of tones and semitones is got. If we take G for instance as the key note, and rise to an octave above it, the first semitone between its 3rd and 4th note happens to coincide with one already there in the scale of C, but the 2nd semitone, to be between the 7th and 8th notes, requires to be made by sharpening the 7th note, F. We thus have the right succession of tones and semitones for the scale of G by making one note sharp. This mark of F sharp is put once for all at the beginning of any piece of music written in the scale of G, and such mark is called the signature of the key.
In a similar way we must alter by sharps or flats the notes of the scale, for any key note we need to write music in, until we have got the right arrangement for the major scale of that particular note. At present minor scales, which have a different arrangement of the tones and semitones, are not considered.
III. The musical interval called a fifth consists of three whole tones and one semitone. For instance, between C and G there is a fifth, G being the 5th note above C, counting each of them :
C, D, E, F, G.
1, 2, 3, 4, 5. In this case the natural arrangement of tones and semitones is right. But, if needed, the notes would have to be altered by sharps or flats to make the interval perfect.
Now we may go to work with this interval, and see what we can get out of it in various ways.
IV. If we write the natural scale of C several times over in succession, and rise from the starting note by jumps of a fifth each, we get a series such as the following :CDEFGABCDEFGABCDEFGABCDEFGABC ve
y 1 2 3 4 5 6 7 Here G is the first fifth above C; D the next above G; and 80 on, till we come to another C, at the 7th fifth above the C we started from.