Search results
Results From The WOW.Com Content Network
The basal condition for mammals is to have internal testes. [51] The testes of monotremes , [ 52 ] [ 53 ] xenarthrans , [ 53 ] and afrotherians [ 54 ] remain within the abdomen ( testicondy ). There are also some marsupials with external testes [ 55 ] [ 56 ] [ 57 ] and boreoeutherian mammals with internal testes, such as the rhinoceros. [ 58 ]
Testicular descent occurs to a variable degree in various mammals, ranging from virtually no change of position from the abdominal cavity (monotremes, elephants, and hyraxes); through migration to the caudal end of the abdominal cavity (armadillos, whales, and dolphins); migration just through the abdominal wall (hedgehogs, moles, seals ...
The intraabdominal testes and excurrent ducts, along with the presence of a cloaca exhibit homology to the reptilian male reproductive tract. [1] [2] The combination of reptilian and mammalian structures within the monotreme reproductive tract has informed the evolution of the male reproductive tract in mammals.
As in all true mammals, the tiny bones that conduct sound to the inner ear are fully incorporated into the skull, rather than lying in the jaw as in non-mammalian cynodonts and other pre-mammalian synapsids; this feature, too, is now claimed to have evolved independently in monotremes and therians, [9] although, as with the analogous evolution ...
The primary sex organs are the gonads, a pair of internal sex organs, which diverge into testicles following male development or into ovaries following female development. [8] As primary sex organs, gonads generate reproductive gametes containing inheritable DNA. They also produce most of the primary hormones that affect sexual development, and ...
The article then goes on to explain that some of these mammals have other thermoregulatory adaptations to keep internal testes cool "Thus, many ascrotal taxa like seals and Catacea have developed specific mechanisms for cooling their testis (e.g. venous plexuses carrying cool blood to the spermatic arteries), whereas others such as Monotremata ...
The hemipenis is the intromittent organ of Squamata, [4] which is the second largest order of vertebrates with over 9,000 species distributed around the world. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. [5]
Most mammals are viviparous, giving birth to live young. [1] However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. [2] In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian ...