SPERMATOGENESIS OF THE PACIFIC COAST EDIBLE CRAB,CANCER MAGISTER DANA

Abstract

1. During the latter part of June and the early part of July the testicular lobes of Cancer magister are in the best shape for the study of spermatogenesis.2. Two spermatogonial divisions can be recognized, and these ultimately form the resting primary spermatocytes.3. Sometimes, larger and more intensely staining cells are found interspersed among the spermatogonia. These are the nutritive cells, and it seems very probable that they have originated from a transformation of some of the spermatogonia. The nuclei of the nutritive cells are irregular in shape and many of them possess amœboid processes. In sections of some of the nutritive cells two or more nuclei are oftentimes found, and this might easily mislead one into concluding that amitosis occurs amongst them.4. The resting primary spermatocyte undergoes a growth period, during which thin leptotene threads are produced through the fragmentation of the chromatin. No continuous spireme is formed as the leptotene threads appear distinct and separate.5. During the growth period pairs of leptotene threads migrate to the synaptic pole of the cell, become arranged in parallel fashion and soon fuse parasynaptically.6. During the synizesis stage of the growth period a pair of densely staining chromatoid bodies make their appearance in the cytoplasm. These are surrounded by clear areas and may have originated from some of the chromatoid masses found within the cytoplasm of some of the earlier stages in the spermatogenesis.7. The first spermatocyte division is reductional. In the metaphase stage the chromosomes line up as dumb-bells, which are composed of pairs of bivalents. The chromatoid bodies pass undivided to opposite poles of the cell.8. A polar view of the metaphase stage of the reduction division reveals sixty chromosomes distributed throughout the entire plane of the equator.9. The division of the primary spermatocytes results in secondary spermatocytes, each of which contains a chromatoid body.10. The second spermatocyte division is equational and immediately follows the reduction division. A polar view of the metaphase stage of the equational division reveals sixty chromosomes which are about half the size of those found during the reduction division.11. The chromatoid body passes undivided to one pole during the division of the secondary spermatocyte, resulting in the formation of two classes of spermatids, one of which contains the chromatoid body, while the other is without such a structure.12. The chromatoid body is soon expelled from the spermatids which contain it, thus making all the spermatids alike in structure and appearance.13. The nucleus of the spermatid loses its large quantity of intensely staining chromatin, while at the same time a mitochondria-like mass makes its appearance in the cytoplasm. Also one or two vacuoles are formed in the cytoplasm.14. As the transformations go on the nucleus becomes elliptical and wanders to one pole of the cell. The vacuoles fuse into a single large vacuole which then takes a position at the opposite pole of the cell. The mitochondria-like mass wanders in between these two structures, becomes ring-like, and within its center and above the karyosome-like body of the nucleus, the centrosome becomes stationed. Soon a second vacuole makes its appearance at the distal end of the first one.15. The two vacuoles gradually transform into the first and second vesicles. The centrosome and karyosome-like body of the nucleus become fused into the central body, which runs through the middle of the second vesicle, while the nucleus and mitochondria-like ring unite into a nucleus-mitochondrial cup from which the rays of the spermatozoön are produced.16. The mature spermatozoa are oval bodies tightly packed within membranous spermatophores.17. When the mature spermatozoa are surrounded with salt solutions possessing a lower osmotic pressure than either the crab's body fluids or sea water, they undergo an interesting explosion in which the vesicles and the central body are completely everted, while at the same time the nuclear-mitochondrial cup rounds out into a spherical structure.