Spermatogenesis of the Domestic Fowl Studied with the Electron Microscope

Abstract

The seminal epithelium of the domestic fowl was studied in thin sections observed with the electron microscope. The results obtained are summarized as follows:
1. The cytoplasm of seminal cells contains a great number of fine granules (microsomes) which vary in density as well as in size from a few to 200mμ. Rough and smooth surfaced Types of the endoplasmic reticulum are observed in the cytoplasm of seminal cells. As the rough ones decrease, the smooth ones increase in number during the differentiation of seminal cells, at least, until the spermatid grows elongated. These observations differ from those on the cat as reported by BURGOS and FAWCETT. The origin of endoplasmic reticulum may be closely concerned with the microsomes connected like a beaded chain, with spindle fibrils and remnants.
2. The GOLGI apparatus of each of all seminal cell types of this animal consists of GOLGI granules, lamellae and vacuoles. The GOLGI apparatus is identical with the‘Idiozom’of light microscopy. It appears that the GOLGI granules are probably equivalent to the S-microsomes of MORITA being scattered in the general cytoplasm, and both the lamellae and the vacuoles of GOLGI apparatus may be developed through the expansion of S-microsomes or from chains of them fusing with each other.
3. Internal structure of the mitochondria observed in this material is extensively variable. Some show the striae, i. e., cristae mitochondriales of PALADE which are seen as a connection of the fine granules in some parts, while others are seen as masses of fine granules or small vesicles. These granules and vesicles may belong to the category of the microsomes.
4. The centrosome observed in the GOLGI area of the resting cells is cylindrical in form and its wall consists of several parallel filaments embedded in the osmiophile substance which may correspond to the A-substance of MORITA. This substance is also found separately, lateral to the wall of centrosome. It appears that this substance is in a ring just like a‘ring centrosome’of the spermatid. The cylindrical centrosome may be transversely divided into two forming the diplosome. In some cases, at one pole of the spindle during the anaphase of the mitotic division, there are two centrosomes, each of which shows essentially the same structure as that of the resting cell.
5. The spindle fibrils are observed as the strands or tubules, and in some parts as a file of small vesicles which are called the S-microsomes. Hence, it may be considered that the spindle fibrils arise from the beaded chains of microsomes, and attaining a tubular appearance, again lose the tubular features or remain as the bead-like strands in some parts, during the mitotic cycle. In this point of view, the author agrees with KUROSUMI's description of sea urchin blastomeres.
6. During the period while the spermatids are maturing, the karyoplasm appears as an aggregation of coarse granules similar to those of the cat and toad as reported by BURGOS and FAWCETT. These granules do not grow into filaments or lamellae as are found in certain animals.
7. The acrosome developes from the granule within a vacuole in the GOLGI apparatus of the spermatid. The tip of the elongated nucleus is found inserted into the acrosome just like a key put into a lock. The acrosome consists of a homogeneous substance and there are no filamentous elements.
8. It is noticed that the origin of the caudal sheath is not concerned with the nuclear membranes but with the beaded strands of the microsomes. The head, except for the anterior part covered by head cap, and the middle piece of spermatid are surrounded by the caudal sheath.
9. Besides a centrosome, it is observed in the late spermatid that the middle piece has a cylindrical shape resembling a centrosome, but is much longer than the latter. It seems that the middle piece may correspond to the‘distal centrosome’, which has been elongated.