Pygidium of a Cat Flea : SEM image needed

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MichaelG.
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Pygidium of a Cat Flea : SEM image needed

#1 Post by MichaelG. » Sun May 16, 2021 7:30 pm

I am currently viewing a box of slides on the ‘Postal Microscopical Society’ circuit.
... One of these is a decent mount of a Cat Flea [in profile]

The ‘pygidium’ is visible, but it is proving difficult to interpret the detail

For those unfamiliar ... the pygidium is a classic ‘test object’ and is discussed here:
http://www.microscopy-uk.org.uk/mag/ind ... -test.html

The problem I think is that the standard ‘test object’ is a top-view, showing left and right patches flattened as shown in the article. ...But, on the the PMS specimen, it is presumably folded in half.
As a test object, we should obviously be viewing the ‘wheel’ structure from the outside ... but what I am seeing is sufficiently confused to suggest that I am seeing both layers.

It would be a great help if I could find a detailed SEM image for comparison ... but my own searches have found nothing suitable.

Can anyone suggest a source, please ?

MichaelG.
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photomicro
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Re: Pygidium of a Cat Flea : SEM image needed

#2 Post by photomicro » Mon May 17, 2021 9:15 am

I rather think you have the reason already Michael, in that to see the pygidium and show the features outlined in its use as a test object, requires it to be mounted especially for that purpose.

Most slides I have, or have seen, are whole mounts, and I guess the mounter wasn't really bearing this in mind as such. Of course, the lovely Watson mount shown by David Walker in his article you referenced, is specifically done for the pygidium to be shown in all it's glory.

Just looking at two slides I have, a Biosil one shows this area rather folded over, whereas another is much better in this respect.

Perhaps a few lines from Spitta (3rd Edition, 1919) may help us here;

"First, in selecting a specimen, care should be taken that it its mounted beneath the cover the correct way up. This is known at once by the simple fact that the long hairs coming from the wheels (to be explained hereafter) should come first into view. If this is not so, the specimen should be rejected, as all the detail of the surface of the pygidium about to be explained will be viewed through the solid portion of the object, which materially spoils the definition."

I am guessing that, like you, when I do a search for SEM images, there are plenty of the whole flea, or the mouthparts, but no rear end !

Mike

MichaelG.
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Re: Pygidium of a Cat Flea : SEM image needed

#3 Post by MichaelG. » Mon May 17, 2021 12:53 pm

Thanks, Mike ... I’m sure your analysis is spot-on

The really strange thing [which prompted my search for SEM] is that as I focus through the specimen it appears that the hairs in the centre of those wheels are slightly twisted flat strips, rather than the cylindrical rods that David Walker describes.

I suspect this is an optical artefact [due in part, perhaps, to my need to close the condenser aperture right down, to see anything much] ... an SEM image might help explain this curious effect.

Focusing carefully, I can see the ‘spoked wheels’ quite well; but they each appear to have ‘twins’ almost directly below them ... this would of course suggest that the pygidium is ‘folded’ rather than having been halved.

Your comments are much appreciated.

MichaelG.
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MichaelG.
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Re: Pygidium of a Cat Flea : SEM image needed

#4 Post by MichaelG. » Mon May 17, 2021 7:14 pm

For any flea fans ... here is a superb [zoomable] copy of the engraving in Hooke’s Micrographia:
https://luna.manchester.ac.uk/luna/servlet/s/02k2ng

Thanks to the wonderful team at the John Rylands Library in Manchester.

MichaelG.
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75RR
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Re: Pygidium of a Cat Flea : SEM image needed

#5 Post by 75RR » Mon May 17, 2021 8:56 pm

MichaelG. wrote:
Mon May 17, 2021 7:14 pm
For any flea fans ... here is a superb [zoomable] copy of the engraving in Hooke’s Micrographia:
https://luna.manchester.ac.uk/luna/servlet/s/02k2ng

Thanks to the wonderful team at the John Rylands Library in Manchester.

MichaelG.
Makes for an impressive if unsettling desktop picture - will go back to the SEM diatom ;)
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photomicro
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Re: Pygidium of a Cat Flea : SEM image needed

#6 Post by photomicro » Tue May 18, 2021 8:19 am

I have now examined around a dozen slides, all whole mounts, and the orientation of, and therefore ease of viewing this structure is extremely variable indeed !

In some, it almost appears like a horse-saddle shape, or Pringle crisp.

I may try to image one of the better ones.

MichaelG.
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Re: Pygidium of a Cat Flea : SEM image needed

#7 Post by MichaelG. » Tue May 18, 2021 9:00 am

Keep up the good work, Mike

Meanwhile, I think I have learned as much as I can from this particular slide ... but will be intrigued to see a specifically prepared test specimen if I can find one.

MichaelG.

.
Edit: There’s a useful photo on page 18 of this : http://science.marshall.edu/joy/Ebooks/ ... k%20v5.pdf
... and I’ve also learned that it’s a.k.a. ‘sensilium’
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Re: Pygidium of a Cat Flea : SEM image needed

#8 Post by photomicro » Wed May 19, 2021 1:29 pm

As you say Michael, the preferred term seems to be sensilium, which I assume it suggestive of a sensory role.

This is from one of the better slides, which as I said are all whole mounts. It is of a mole flea I think, Hystrichopsylla talpae, in this case, a female.

Whilst the area of interest here is still rather folded, it does show some detail.

All those tapered hairs don't help in stacking, and is often the case, you learn more when viewing through the microscope as you use the fine focus.



mole flea female 1.jpg
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