Schematic diagram of the Malacabdella grossa spermatozoon and its acrosomal region and neck region.

(A) Acrosome

(AN) Annulus

(AV) Acrosomal vesicle

(DC) Distal cenriole

(M) Mitochondrial sheath

(N) Nucleus

(PC) Proximal centriole

(PR) Post-acrosomal ring

(SA) Subacrosomal material

(T) Tail

With these considerations as a background a fine structural investigation was started using the sperm of the parasitic nemertine Malacobdella grossa (O. F. Müller). The sperm of this species can be characterized as advanced as evidenced by the studies of Retzius (1904) and Franzén (1956). The mode of fertilization is incompletely known.From: The spermatozoon of the nemertine Malacobdella grossa Bjorn Afzelius J. Submicro. Cytol., 3, 181-192, 1971(A) Acrosome (AN) Annulus (AV) Acrosomal vesicle (DC) Distal cenriole (M) Mitochondrial sheath (N) Nucleus (PC) Proximal centriole (PR) Post-acrosomal ring (SA) Subacrosomal material (T) TailWith these considerations as a background a fine structural investigation was started using the sperm of the parasitic nemertine Malacobdella grossa (O. F. Müller). The sperm of this species can be characterized as advanced as evidenced by the studies of Retzius (1904) and Franzén (1956). The mode of fertilization is incompletely known.