Spermiogenesis in the tick, Amblyomma dissimili, as revealed by electron microscopy

Observations on the endoplasmic reticulum (ER), nucleus, and acrosome of developing spermatids in the tick Amblyomma dissimili are reported. In early spermatids the ER consists of branching, tubule-shaped cisternae. In later stages the ER lacks attached particles and takes the form of spheroid cytomembranes, which eventually become flattened and arranged as whorls around mitochondria of mature spermatozoa. in early spermiogenesis the nucleus comes to lie at one pole of the cell where an acrosomal vesicle becomes situated. As acrosome formation proceeds, nuclear chromatin aggregates into electron dense chromatin threads that eventually fill the entire nucleus. The acrosomal vesicle becomes flattened between the nucleus and cell membrane in early spermatids and expands as a flat, dise-shaped acrosome. As spermatids elongate, the acrosome is pulled in upon itself into a U-shaped structure. In the mature spermatozoon the acrosome and nucleus are situated in the tail. Comparisons of these findings are made with respect to the early light microscope studies on spermiogenesis in ticks and with recent electron microscope studies of spermiogenesis in other forms.