Abstract
The heart creates positive and negative pressure in a
regular rhythm to pump blood. The cardiac chambers
seen in vertebrates are an advanced pump design. Many
species, such as the hagfish, still have accessory pumps,
but they are considered vestigial. Additionally, the
processes by which the circulatory system develops in
vertebrates, including heart development, are largely
unknown. In this study, we examined the heart of hagfish
(Eptatretus burgeri) using histological analysis. In E.
burgeri, three types of hearts were observed: branchial,
cardinal, and portal. Photomicrographs showed that there
are many empty spaces in all three types. These hearts
pump blood in and out of the sponge to absorb and
discharge water. The cardinal heart near the brain in E.
burgeri may be primitive because its cell structure is
similar to that of skeletal muscle.
