The testes are the male dog's reproductive glands that normally start off positioned in the abdomen as embryo development progresses during pregnancy. They normally travel down through the abdomen from their initial location near the kidney, out through the inguinal ring in the groin, into the scrotum soon after birth.
All puppies are born with their testicles up in the abdomen. Normally by the time the puppy is 6 weeks old both of the testicles have descended into the scrotal sack. However in the case of cryptorchidism one, or both, of the testicles fail to come down into the scrotal sack and remain in the abdomen.
The treatment for retained testicles is castration. This procedure is highly recommended because retained testicles can sometimes become infected or cancerous. If a dog only has one testicle retained, and the owner wishes to breed the dog, than the retained testicle can be removed and the other testicle left alone. Though the owner needs to be aware that the dog’s puppies may have the disorder as well.