Tarantulas can be sexed ventrally but it's not a foolproof method, the only 100% way to sex a tarantula is by examining the exuvium and ascertaining wether there are spermathecae present proving that it is female....
Here are a few helpful pics:

Firstly there's a very informative article on Rick West's tarantula site concerning ventral sexing and here are a few pics taken from there and the link...



Link to Rick West's article




Firstly the male where there's no female organs visible





In the female the uterus externus (flap) and spermathecae would be present





and viewed from the front of the tarantula the spermathecae in closeup isolation can also indicate species as can be seen from these 3 examples, notice how different they can be...

Thanks I just sexed my one Ts this mornign usen the exuvium and Im delighted to say its a female But i shall wait and see my luck of geussing turns out ...

And then what is your guys feelings on holding the Ts as alot of amercains do and the peeps do in the UK ..


And then some thing i have read on another forum was the space between coxa but here is a link to this page what do you guys think about this .. www.atshq.org/forum/showthread.php?t=12742&page=7

Personally, not a ventral person myself...

This is a very basic description. More experienced keepers can elaborate.

Definition: Spermatheca - (Singular) Spermathecae (Plural)

A receptacle in the reproductive tracts of certain female invertebrates, especially insects, in which spermatozoa are received and stored until needed to fertilize the ova.

How to find.

Once the spider has moulted, carefully remove the exuvium from the container. Do this ONLY once the spider has turned back on it's feet and has moved away from the exuvium. Take great care NOT to desturb the spider unnecessarily, as the new skin is very soft at first.

Try to "open" the abdominal skin so a clear view of the inside is obtained.

In the case of females, the spermathecae will be positioned between the anterior booklungs, always exactly in the middle of the skin between the booklungs and slightly above the bottom of the booklungs.

In some species, the spermathecae are fused, meening there will only be one structure visible.
In some species, the spermathecae are paired, meening there will be two structures visible.

In the picture here, the spermathecae are paired.



Also refer:

Spermathecae gallery

i think this is really interesting and im sure you guys will to

www.arachnophiles.co.uk/forum/showthread...Spermathecae-Gallery