19 March 2006

Dissection IV: Dogfish Shark

Without a doubt the coolest dissection yet, especially because our TA returned (there was a sub last time) and there was no lab quiz. We dissected the dogfish shark, right down to cutting open the skull and stomach. The stench was, well, it was powerfull and there was definately some projectile sperm while examining the male reproductive organs, but for the first time you could really see the homology between the dissection subject and well, our future patients.

The liver was stunning. Not because it was elegant, but because it was huge and so luxuriously slimy. Since it's largely lipids it has this sleek sheeny texture. The kidneys were unusual since they are on the abdominal wall surface and run the length of the shark. Even more interesting is that the vas deferns (sperm transport ducts) are on the surface of the kidneys. Sperm travels though the kidneys and then the vas deferns to the seminal vesicles which leave the shark throught he cloaca (think: anus) and travel into the female on one of the two claspers.

Ah... and here's the good bit. The male shark has TWO claspers. What do they do? Well, one of them penetrates the female cloaca, hooks itself in there, delivers the sperm, and then releases. What this means is... the shark has TWO penises. Call me 15, but I think that is... unusually well endowed?

The brain was also the most developed we've seen to date... in three distinct sections. Carving off the skull piece by piece was quite the task though - it took us about 20 mins, but we managed to keep the brain in tact, including all the olfactory bulbs. I did finish the afternoon with rather a long shower though because formaline is such a cloying perfume.

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