part_of adult body adult male reproductive system adult testis Fig. 17-1, Fig. 17-2, Fig. 17-3, Fig. 17-5, Fig. 17-6, Fig. 17-7, Fig. 17-8, in Biology of Ticks ISBN:0-19-505910-7. Most ticks have a pair of elongated, tubular testes connected near the midline of the body by a thin isthmus. Each testis is a tubular organ comprised of layers of germinal cells surrounded by a thin connective tissue membrane and occasional smooth muscle cells. Interstitial cells occur primarily along the luminal border, according to Raikhel (1983). Spermatogonia, primary and secondary spermatocytes are grouped into clusters termed spermatocysts. Each cluster contains 32 - 64 secondary spermatogonia or spermatocytes, depending upon their position in the testis, and surrounded by a narrow lumen.The testes enlarge greatly during feeding. TADS:0000461 TADS:0000461 default_namespace simple organ