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Книга по требованию: Science-Gossip (Classic Reprint)

Товар № 11450713
Вес: 0.09 кг.
Год издания: 2015
Страниц: 46 Переплет: мягкая обложка
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Excerpt from Science-Gossip

I think all the members of the family are vegetable feeders, and may be seen grabbing with the "pack" among Confervae and decaying water-weed. The mastax is also extruded on the ventral surface - there is a bend of the carapace for this purpose - and may sometimes be watched nibbling at the surface of a weed. The cilia as usual are used to create currents, bringing streams of sediment into the mouth, and in swimming.

I kept the water by me, examining it from time to time, always finding fully grown individuals (figs. 9 and 10); but with these were other forms, smaller and of different outline. As time went on some Philodina made their appearance, the Metopidia decreased in size, then in number, until on the 7th of April, from a dip that would a month previously have produced hundreds, I could only find one, which is of the shape shown in figs. 7 and 8; also five or six Rotifer vulgaris, two or three Philodina citrina, and several Monostyla lunaris. I also found Callidina parasitica, which I was puzzled to account for till I observed an Assellus creeping among the decaying weed at the bottom of the jar on April 20th. The Callidina had left the body of the host, and in their independent state were certainly thriving and many in number.

At first I was inclined to regard the various forms of Metopidia as different species, but watching the appearance of a young one from the egg (figs. 1 and 2), I was puzzled by its great difference in outline from the parent species, and by the presence of short spines at the base of the carapace, which I regarded as a specific characteristic. This young one was 1/300 of an inch in length. It took nearly three-quarters of an hour to wriggle free of the shell. The carapace was not well marked, the body was granular and semi-opaque, and it was decidedly cylindrical in shape. The form that seemed most nearly allied to this is that figured as 3 and 4, which appears not unlike the M. rhomboides of Hudson and Gosse. Its length was 1/200 of an inch. The lateral view shows that the body has not properly developed into the lorica, but still retains much of the shape that characterised the young one when it issued from the egg. There are no signs of the spines at the base of the carapace, they apparently having been absorbed. More plentiful than this form was the oblong one figured as 5 and 6. The length of this was 1/200 of an inch, but it was exceedingly thin, and consequently very difficult to keep still in a live-box. This possibly may be Squamella oblonga.

It was at this stage that the chief difficulty of my investigation commenced. In this, which I conjecture to be the third form, there are no spines at the base of the carapace: they reappear more marked than ever in the fourth, again disappearing in the full-grown rotifer.

The fourth stage is figured as 7 and 8, and has been familiar to me for years. Its length is still 1/300 of an inch, but it is distinctly more solid. In every detail, with the exception of the base of the carapace, it agrees with the final form (figs. 9 and 10), which has reached a length of 1/123 an inch, and is, I understand, to be found still larger. The male made his appearance, after some time, on February 17th (figs. 11 and 12). He was 1/225 of an inch in length, and, like all male rotifers, very restless and active.

The ordinary egg is quite plain (fig. 13), but after the males had been seen, the "resting egg," or so-called "winter egg," was found covered with minute spines and about 1/300 of an inch in length.

I am led to think that these are all stages in the growth of the same species, for the following reasons: (1) At one time there were no rotifers present except the fully grown form; (2) the very fairly good though accidental isolation not complete, as the appearance of other genera proves; (3) the known variety of form in the young of this genus; (4) all details, pick, eyes, mastax, place of.

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