Repro. System - Male

Like other mammals, the male reproductive tract of the harbor porpoise and other cetaceans consists of two testes with epididymides (singular epididymis), vasa deferentia (singular vas deferens), prostate, and penis. Unlike many mammals however, the testes are located within the body wall (intra-abdominal) and lack a scrotal sac (this is different than in the sea lion).

The penis is also retractable, and unlike pinnipeds, sea otters, and polar bears, cetaceans lack a baculum, or bone within the penis. The penis is surrounded by two large muscles (blubocavernosal muscles) which push the penis out of the body during mating. The penis, along with these muscles, form a raised structure on the inside of the abdominal wall, upon which the bladder sits with the testes flanking each side (see below).  

One of the most interesting aspects of cetacean male anatomy is the specialized circulatory anatomy that maintains the testes several degrees below body temperature, a condition necessary for sperm production. The blood vessels that are surrounding the testes are coupled to veins returning blood that is coming directly from the superficial blood vessels of the dorsal fin and fluke, thermal windows which allow the blood to cool down considerably. The cooled blood is directed around the testes, isolating them from the heat produced by the surrounding swimming muscles and viscera of the abdomen. Similar structures help keep the fetus cool during pregnancy in the female cetacean.

During necropsy, the presence of sperm in the testes or epididymides confirms sexual maturity and one set should be collected and fixed. Alternatively, complete cross sections should be collected and fixed in 10% buffered formalin. Other measurements that are often collected include the mass of one testis and epididymis weighed separately as well as the height and length of the testis. Note that the testes of most cetaceans undergo extreme seasonal changes in the size. In some species they can more than double in size during the breeding season then contract back down in size for the remainder of the year.

For more information about male reproductive anatomy or the circulatory structures described above see Rommel et al., 1992 and 1994, Pabst et al. 1995 as well as The Biology of Marine Mammals (Reynolds and Rommel Eds., 1999).

Detailed annotated images of the male reproductive system in a harbor porpoise are shown below.  CLICK on an image to see an enlarged view.