21 November 2006

The naughty bit of a snail

The ruler is in millimeters. The verge is about 3 mm long. (e: epiphallus, v.d.: vas deferens.)

This is the inside of the penis of a specimen of Xerocrassa cretica, a land snail in the family Hygromiidae that lives in western Turkey and some of the Greek islands in the Aegean Sea.

I spent several hours this afternoon and early this evening dissecting, positioning & photographing the genitalia of this snail for a manuscript I am writing about it.

During mating, the snail's penis, normally kept inside its body, is everted, very much like the turning inside out of the finger of a glove. So, during a dissection, to see what the outside of a penis looks like, one needs to cut open the penis and look inside it.

On the inside of a penis that becomes the outside during mating (confusing, eh?), there is usually a projection called the verge (= penile papilla). Once the penis is everted, the verge becomes the tip of the penis and thru which the sperm is transferred.

The tip of the verge of Xerocrassa cretica is highly convoluted and deeply folded. So is the inside wall of the penis. I spent most of my time trying to capture that morphology in my photographs.

To take the photograph I used my Olympus E-500 with a Zuiko 35 mm macro lens and an EX-25 extension tube. The extension tube was necessary to obtain the proper magnification, but it left almost no room between the front of the lens and the subject for lights. I had to light from the side. That, however, wasn't possible with the aluminum dissecting dish I was using. So in the middle of all this, I had to make a new dissecting dish with glass sides. Luckily, I had a small Pyrex petri dish. I put some black wax in it, put it in the oven for about 5 minutes to melt the wax and 10 minutes later, the new dissecting dish was ready.

Later, while examining the picture on the computer screen, I noticed that the pin on the right had cast a long shadow across the wall of the penis and along the edge of the verge. Now, I am wondering if I should re-photograph it.


Rudko said...

I know nothing, being just a layperson, but it looks like a great photo to me.

I had a hard time identifiying the pin you had the problem with so maybe just identifying it in the caption is enough.

clare said...

Highly impressive photo, I would say. I don't the shadow detracts from it at all - it actually might help to give a little more impression of depth IMHO.