I need your commentary about this lesser enchantement
The Priape's Jar
Creo Corpus
Range : Touch
Duration : Sun
Target : Ind
Preserve the vitality of the semen. The semen keep it fecondity and permit the conception at the condition
to be put inside a fertile woman.
Base 2 (Préserve a corpse to rot) +1 Touch +2 sun +1 2 uses per day +3 environnemental trigger (sunrise, sunset).
Level 9 1 pawn of vis
Hm. 3 thoughts:
The semen in question would be under a constant magical effect, which means it would be picking up 2 points of warp/year. After 2 1/2 years, you're using officially Warped semen - your GM may use that to engage in additional stories.
Is (functional) artificial insemination a thing? This is a point at which I don't know enough about medieval biology to know whether or not it would actually fit into the rules of Mythic Europe.
Is semen considered dead? If not, I'd say it probably should be something a bit higher. (But again, this plays into "what is semen considered to be in ME biology?") However, if they are analogous to seeds, then "keeping living seeds fresh" probably isn't much higher (maybe +1 magnitude?)
Well, a slight variation may be to have the enchantment in your Familiar link (which doesn't cause warping? I forget.) - and have it be on you BEFORE you start taking your Longetivity serum. This would essentially be a sort of MuCo effect, whereby you'd have a resivoir (essentially a 3rd testicle) that had a limited supply of non-Longified-but-still-fresh semen.
...and hey, that's a sentence I never thought I'd write...
EDIT - in thinking about it a bit more, I think there starts to be a blurring between "what is a Longevity ritual" and what is keeping a part of me fresh". Arguably, you could probably claim that the effect you're describing IS a variation of a longevity ritual, in that you're trying to get a living part of your body to not age. As such, if someone were to not like this effect, they'd probably argue that.
Personally, I don't have a real problem with it, as long as the expiration date is within a normal human lifespan (ie, the biblical "70 years"). So, it would let you have kids for a few decades after you started up the LR. From a game mechanic/storytelling perspective, don't see a problem with that. Of course, it's not guaranteed that it will work (ie, pregnancy doesn't always take on the first attempt), and you've only got a few chances before you run out. But as a chance to have a kid later on in life? Eh, sure.
(Of course, the immediate question is "OK - how about you just have a kid before your 35th birthday? You're only getting another 30 year's delay out of it, with the added irritation of having to have a 3rd tentacle."
The semen is stored into a jar of glass or other material. Right, the semen must be recuperate before the longevity ritual.
The semen is under an effect inferior as 2 magnitudes. It is too low to cause warping. You're right the pregancy is not garranty.
In ME biology the semen is known to be the fecondant part of the men (It is known since Roman Empire). The semen could be introduce with the help of magic (rego aquam or corpus) or a syringe.
A take a base 2 "Preserve a corpse to rot" because when the semen is out of the body, the semen is dying.
Can you cite your source on that? I've got AM5th. pg. 168. "A character who is constantly under the influence of one or more active mystical effects gain one Warping Point per year for each effect. The strength of the effect is irrelevant, as is the caster, and whether or not the effect was designed specifically for a certain person."
OK - so it's just 1 point/year, rather than 2. From what I recall, this affects everything (not just characters) - it's just that it's normally not interesting to track it for everything, so mostly it just gets put in as background flavor (or in amusing accidents in your Lab, via the Covenent rules). However, in this case, it's arguably still a part of the character, in the same sense that keeping a severed limb alive is still part of the character (or at least, interesting enough to use the standard Warping rules). As such, it would probably pick up warping as well.
Yes, but it's not dead yet. To keep something alive is more akin to "Prevent a target's wounds from getting worse" (Base 3); probably +1 part, due to the fact that it's a specific part/fluid of the body. In contrast, a corpse is dead - you're just preventing decomposition.
For the warping AM p168
.
But you're right. The effect is constant and the semen gain 1 warping point per year.
Base 3 "Prevent a target's wounds from getting worse" makes more sens.
Part to me is not appropriate the semen is no more reliate physically to the body. The semen is stoked in a bottle.
The Priape's Jar
Creo Corpus
Range : Touch
Duration : Sun
Target : Ind
Preserve the vitality of the semen. The semen keep it fecondity and permit the conception at the condition
to be put inside a fertile woman. The semen gain 1 warping point per year.
Base 3 (Prevent a target's wounds from getting worse) +1 Touch +2 sun +1 2 uses per day +3 environnemental trigger (sunrise, sunset).
Level 14 2 pawn of vis
By the way, the magus will keep that well hidden as it is definitely a strong arcane connection to himself. And the enchantment will kind of act as a stabilizing effect on the arcane connection.
And a magus designing such item might have been inspired by how some homonculus are made. One of the description I found (in the occult literature, but I cannot remember the reference) was that the alchemist trying to make an homonculus, must collect all kind of components from his body (blood, hairs, dead skin, feces...) as the first phase to make the homonculus body. I do not remember the next part, but afterwards, once the homonculus is born, he needs to feed him with his own blood every day, similarly like a baby would suck milk from her mother.
That's the price to pay to have your own "descendant" - kid does not seem appropriate to describe the homonculus. This looks very much like a purely magical way to make one homoculus (compare to the one from RoP: Faerie and the homonculus magi, but quite different origins and needs).
My observation is that the targets should probably be 'Part', rather than 'Individual'. A severed arm is still a part of a corpus, not a corpus itself. The same with, uh, expended semen. It's still quite a clever idea. While the numbers seem to work out, I wouldn't be surprised if some storyguides would link the sterility to the Longevity Ritual, and the seed is part of the body, and the two are mythically linked by God, or somesuch, ruining your plans. That said, it would be a fun story point, but I wouldn't want a set rule on it.
Well, canonically, the sterility aspect of the LR is a flaw in Hermetic Theory, rather than a Limit of the Divine. (Although I agree that it sorta sounds like one.) It's fixed using Original Research in...Magi of Hermes, I believe. (Or at least, it's a goal for one of the characters to fix the sterility aspect, and in their own timeline they successfully use OR to create a minor virtue that does so.)
Just because the mortal mages think its a flaw in Hermetic Theory doesn't mean it is one. 
New plan to irritate Bonisagus in the making...