ULTRASTRUCTURE OF THE MALE GONAD AND SPERMATOGENESIS IN THE LESION NEMATODE, PRATYLENCHUS PENETRANS (NEMATA, PRATYLENCHIDAE)

Transmission electron microscopy was used to elucidate the structural anatomy of the male reproductive system of Pratylenchus penetrans. The male gonad has an elongated telogonic testis with a single row of spe rmatogonia in the germinal zone. The spermatogonia increase in size to spermatocytes in the growth zone. The spermatocytes then undergo meio sis to form spermatids. Synaptonemal complexes in the spermatocytes si gnify the pachytene stage of the first meiotic division. Spermatids ar e characterized by an abundance of fibrous bodies surrounding prominen t electron-opaque spheroid nuclei. Spermatids in the proximal region o f the seminal vesicle are transformed to spermatozoa as they accumulat e in the seminal vesicle. During this process, filopodia decrease in n umber, residual bodies are lost, and sperm nuclei become irregularly s haped and surrounded by mitochondria and fibrous bodies. Spheroid sper matozoa retain a modified morphology with large sectors of flocculent cytoplasm devoid of cellular organelles. The electron-transparent regi on of the sperm extends into a pseudopod that controls the crawling fo rm of motility that is typical of the spermatozoa of many nematode spe cies. Seminal fluid produced by cells of the vas deferens accumulates and appears to cause aggregation of sperm within the seminal vesicle. Sperm morphology in the spermatheca of female specimens is similar to that in the vas deferens of the male.