A Study of the Yolk (Y-granules) of the Male Germ-cells
Authors: Muliyil J. A. 
Published: April 2021

Recent researches have established that the Y-granules exist as a fundamental part of the constitution of the male germ-cells of many animals, vertebrates as well as invertebrates. Prior to the application of vital staining techniques to cytological problems, Saccocirrus was the only animal in which these granules were known to exist. The fixatives generally used by cytologists, especially those containing acetic acid and other fat solvents, are not indicated for studying the Y-granules. Vital staining techniques offer the best method for their study. Underfeeding and starvation of the larvae of Agrotis segetum and Abraxas grossulariata revealed that these granules are products of normal metabolic activity, and that their appearance and disappearance depend on the general physiological status of the animal. In normally fed larvae the Y-granules were invariably present, and responded to the vital dye within a few minutes of its application. The germ-cells of underfed larvae showed a steady decrease in their Y-granule contents, as did starved larvae up to a certain stage. When starvation was prolonged the granules disappeared from the cell. The changes produced by underfeeding and starvation in the cell, both in the Y-granule content and the colloidal state of the cytoplasm, were decidedly more pronounced in the spermatocytes than in the spermatids. In very advanced stages of the cell scarcely any change was perceptible. The chemical composition of the granules was determined by studying their reactions to certain vital dyes and fixatives. Neutral red, brilliant Cresyl blue, and Nile-blue sulphate were successfully used to stain the granules, Nile-blue sulphate being particularly satisfactory. This stain is specific for fats and substances chemically allied to fats. Y-granules are composed of either fatty acids or a mixture of fatty acids and neutral fat, because they always stain blue with Nile-blue sulphate. Fixatives containing osmic acid failed to stain the granules except in rare cases when they appeared brown in the preparations. As a rule they appeared a shade of pale grey. As this is a reaction for saturated fatty acids it is believed that in the majority of cases where in fixed preparations the granules are seldom visible, they are composed of saturated fatty acids. The fatty nature of the material was confirmed by fixing testis smears in formalin vapour, and staining them with Herxheimer’s solution of acetone and scarlet R. If the preparations are counterstained in methylene blue the Y-granules are clearly seen stained pink—a reaction indicating the fatty acid nature of the granules. An examination of the ovaries of Abraxas grossulariata, Gryllus domesticus, andLithobius forfi- c a t u s, supravitally stained in neutral red, revealed in every case a juxtanuclear aggregate of neutral red staining granules. With the growth of the oocytes the granules wandered into the cytoplasm and gradually developed into small spheres; their substance simultaneously underwent a chemical change. By the aid of Nile-blue sulphate it was possible to ascertain that the fatty acid contents of the granules gradually changed into fat, or rather into fatty yolk. The behaviour of the granules in the oocytes suggest that the Y-granules in the spermatocytes are only abortive yolk granules having no function under normal conditions. But a gradual reduction in their number, observed in several spermatocytes when the animals were starved, suggests that under exceptional circumstances there is a possibility of the granules exercising some sort of storage function.