[Wuxiong]

As the Imperium has many organisations, who is in charge of desecting Xenos and Aliens? I would imagine that the Apothecarium would be for the Space Marines but what about the Imperial Guard in particular?

 

[Stradius]

the Medicae would do it for guard, but those sorts of things generally fall under the purview of the Ordos Xenos of the inquisition.

 

[Xerxes]

I'm not sure the guard or the space marines would WANT to dissect anything, to be honest... why do they need to? They're filthy xenos. About the only people who might be interested are the Ordo Xenos as said, or a possibly heretical Magos Biologis from the Adeptus Mechanicus. Although maybe not that heretical, given Xenology. But I can't see anyone else being interested in dissections.

 

[Da Mighty Camel]

There's an organisation under the AdMech who handles the analysis of Xeno biology to better combat them. What were they called again...

 

[Dawnrunner]

It would be either the Magi Biologis or the Magi Genetor. The Magi Biologis are almost single-handedly responsible for the Imperium's in-depth scientific knowledge of Tyranids and their biology, and I'm not sure how that would happen if they didn't cut open a lot of Tyranid bodies to find out how they work. The most well-known xenologist dissector, I'd think, would be Magos Biologis Locard. He was attached to Inquisitor Kryptmann's retinue during Hive Fleet Leviathan's attack on Tarsis Ultra, and he created the gene-virus that Uriel Ventris and the Deathwatch shot into the fleet's Norn Queen.
Also, the Imperium wouldn't know that Tau blood uses cobalt instead of iron to bond oxygen, which gives it its blue color, or that Orks are semi-fungoid and reproduce through spores, without dissection and biological study.
So if a regiment of the Imperial Guard came across something that merited attention, the Magos Biologis would probably be the ones who responded.

 

[Wuxiong]

I think Dawnrunner's answer seems the most accurate. But thanks everyone. You all have been a great help. =)

 

[Dawnrunner]

Quick addition-- just read a passage in Graham McNeill's book Courage and Honor that talks about an AdMech "xenolexicon servitor", which provides translation for various alien languages. It does this with the help of a mechanical mouth that rearranges and uses different parts to mimic the shape of various species' speech organs. A character wonders how the techpriests knew what the inside of an alien's mouth looked like, and then shrugs and guesses they cut one open to find out.

 

[ze_poodle]

The Inquisition is the only institution that actually has a reason to catalogue alien biology. Space Marine chapters might undergo independent research if they make fighting that particular alien their special thing. I'd imagine all Marines would have access to the biological knowledge necessary to most effectively kill Alien X, but that's really a limited focus.

I don't imagine the Guard would involve themselves very much in it at all. They're not known for their high-quality training, really. The Inquisition would as a matter of course, and Space Marines would do it because they're master warriors and may well be fighting these aliens for centuries.