THE TAMMAR WALLABY (MACROPUS-EUGENII AND THE SPRAGUE-DAWLEY RAT - COMPARATIVE ANATOMY AND PHYSIOLOGY OF INGUINOSCROTAL TESTICULAR DESCENT

Inguinoscrotal testicular descent in the tammar wallaby (Macropus euge nii) and the Sprague-Dawley rat was studied by macroscopic dissection, histological evaluation and organ culture bioassay. In 3 or 4 d Sprag ue-Dawley rats (n = 10) the gubernacular tip bulged free from the surr ounding tissues, particularly with the application of abdominal pressu re. Microscopic examination revealed that only the body of the guberna culum is connected posteriorly to the pubic region. In contrast, macro scopic dissection of male tammar wallabies (n = 17) revealed a densely adherent distal gubernacular attachment to the inside of the fibrous scrotal bulge while the body of the gubernaculum was less firmly attac hed. These attachments were present throughout the process of testicul ar descent, illustrating an important anatomical difference between th ese species. The gubernaculum from the tammar wallaby pouch young was studied in organ culture with rat calcitonin gene-related peptide for 4 d. Rhythmic gubernacular contractions similar to those documented pr eviously in the rat were not observed. The hypothesis proposed in the rat for the control of inguinoscrotal gubernacular migration via the g enitofemoral nerve and its neurotransmitters may not be applicable in marsupial mammals.