My 4-month kitten has no testicles. Is that why he won't poop in the litter box?

Housecats typically have their testicles descend fully into the scrotum by six to eight weeks of age, but it is not unheard of for this to be delayed for up to a few months in some instances. I would not operate under the assumption your kitty is a cryptorchid (no testicles in the scrotum) at this juncture, but would continue to monitor for their presence on a regular basis. Sometimes one testicle will descend but not the other. In cases where there is no sign of testicles in the scrotum and a client still wishes to neuter, testicles must be found within the abdomen or inguinal region of the body and removed surgically. This is not an extremely common procedure, but certainly one that most veterinarians will do at least a few times during their careers. It is obviously more difficult than a regular cat neuter, since you don't know precisely where the testicles are located anatomically. Anyway, my advise is that you should keep checking and be sure to have your vet verify your findings. Sometimes their testicles can be extremely small at this young of an age. Hope this makes sense.