Testicular Descent in the Dog

The mechanism underlying the process of normal testicular descent in the dog has been examined by a morphological, histological and histochemical analysis of testis and gubernaculum during the period from the 53rd day post coitum (p. c.) until the 40th day post partum (p. p.). Within this period, the testis passes the inguinal canal on the third or fourth day p. p. and reaches its scrotal location on the 35th day p. p. During the entire period the histological composition of the testis (volume percentage of seminiferous tubules, volume percentage of Leydig cells, diameter of seminiferous tubules, number of germ cells) is fairly constant. The △⁵-3β-hydroxysteroid dehydrogenase activity in the Leydig cells before birth suggests a steroid synthesis. Outgrowth and swelling of the gubernaculum occurs until the fifth day p. p. but morphological, histological and histochemical data indicate an onset of gubernacular regression during the last phase of the outgrowth reaction. The migration of the testis from the caudal end of the kidney towards the inguinal canal is associated with the outgrowth of the gubernaculum; during the phase of gubernacular regression, the testis moves from the inguinal canal towards its ultimate location in the scrotal pouch.