Herdmania is hermaphrodite or bisexual, but protogynous so that self-fertilizations is ruled out.
Two large gonads are embedded in the mantle and bulging into the peribranchial or atrial cavity.
The right gonad is situated just parallel and dorsal to pericardium while the left gonad lies within the intestinal loop.
Structure of a gonad:
Each gonad is lobulated and possesses 10 to 25 distinct oval or rounded lobes arranged in two rows one on either side of the central axis.
Each gonad measures 3 to 4 cm long, 1 cm wide and 2 to 3 mm thick. Each lobe is made of a larger, brick red, cortical peripheral or outer testicular region and a smaller, pinkish, medullary or inner ovarian region.
The testicular zone is made up of closely packed spermatic caeca or tubles linked by germinal epithelium, which produce spermatozoa.
The ovarial zone has a lobulated surface to form ovarian follicles containing rounded ova in various stages of development.
Each gonad has two gonoducts, one oviduct and one spermatic duct running along the central axis.
The ovary of each lobe opens into oviduct by its ductule. The oviduct in its turn opens into cloaca or dorsal atrial cavity, through an oviducal aperture guarded by four thick lips.
In the same manner the spermatic duct runs along the oviduct and opens independently into cloaca through spermiducal aperture. Both the gonoducts are lined by cilia internally.
A mature spermatozoa or sperm is microscopic, about 4 p. in length. It consists of a nucleated head capped by a beak-like acrosome in front, a middle piece or neck and a very long straight tail.
Sperms are polymorphic with at least three types, on the basis of length of acrosome whether it is shorter, equal, or longer than head.
A mature ovum is large about 0.3 mm in diameter. It contains a considerable amount of yolk in the cytoplasm.
Three membranes surround the ovum consequtively.
(1) Vitelline membrane
(2) Inner chorion and
(3) Outer chorion