Abstract
Spermiogenesis in the lovebird Uroloncha striata var. domestica Flower was studied with emphasis on microkaryosomes and the origin and development of cytoplasmic microtubules. Microkaryosomes have been clearly observed in all early spermatid nuclei. Utilization for the formation of paracrystalline nucleoproteins is suggested by the fact that microkaryosomes are no longer visible in the advanced spermatid nucleus showing parallel fibrillar elements in the long axis of the nucleus. The plasma membrane of spermatids plays a prominent role in the morphogenesis and organization of the thin-walled, cytoplasmic microtubules; there is no relationship with the nuclear envelope and centriole. Microtubules arranged in regular array are separated by a single-layered membrane to form several layers. The final microtubular bundle develops to surround the sperm head and middle piece; it is a left-handed single helix. The microtubules not only provide a supporting skeleton for a long flagellar type sperm, but may also provide the motive force for the sperm. Thick-walled microtubules are found in the nutritive cells, and are thought to be an apparatus for transportation of nutritive material to the developing spermatids.
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