This study was performed in Fox terrier dogs. Their mean body weight at birth is 315 g; it reaches 12 kg at 1 year of age. The body growth pattern has a sigmoid appearance with a rapid growth phase between 9 weeks and 24 weeks of age. With frequent radiographic examinations, 39 ossification centers were individualized on the long bones; they had all appeared by 25 weeks of age. The fusion of these centers is achieved between 36 and 44 weeks of age. This determination of the bone age has not proved to be a good factor to date the morphologic events of puberty. The testicular width measure is a reliable criteria which is well correlated to the other morphologic and spermatic criteria (volume of ejaculate, spermatozoa concentration). The testicular growth is rapid (width: 0,6 mm/week) between 22 and 36 weeks of age. The first spermatozoa are observed at the end of this period (32 to 34 weeks of age). During the post pubertal period, from 34 weeks to 45 weeks of age, volume of ejaculate, motility, spermatozoa concentration increase and percentage of dead spermatozoa and abnormal forms decrease.