AN ULTRASTRUCTURAL STUDY OF THE TYPICAL SPERMATOGEN ESIS AND MATURE SPERMATOZOON OFCIPANGOPALUDINA CHINENSISGRAY

Cipangopaludina chinensis Gray,a kind of familiar e conomic freshwater snail,was seldom studied in its breeding biology.In the prese nt study,the ultrastructure of the typical spermatogenesis and mature spermatozo on was studied with light microscopy,electron microscopy and cytochemical method to provide scientific data for the future artificial breeding ofCipangopalud ina chinensisGray. It was found that,according to the changes of the structure of chromatin and the morphology of cell,the typical spermatogenesis could be divided into five stage s. They are spermatogonium, primary spermatocyte,secondary spermatocyte,spermatid and mature spermatozoon. At the stage of spermatogonium,the shape of cell and nucleus was not regular. Nucleolus existed in nucleus and cytoplasm had only little granular mitochondria and few endoplasmic reticulum vesicles.Primary spermat ocyte and its nucleus approximately took on elliptical shapes.Nucleus had two layers of membrane and the clearance between them was narrow. Endoplasmic reticulu m vesicles became more,and mitochondrion became more and larger and began to gath er at the posterior of cell and nucleus had synatonemal complex.When secondary s permatocyte,cell and nucleus presented elliptical shapes,nucleus still had two l a yers of membrane and the clearance was wide,part of mitochondrion began to amalg amate, and endoplasmic reticulum vesicles became larger.Spermatid was the most complex changing stage in the whole process of spermatogenesis,which could be fur ther divided into six stages. At the early stage of spermatid cell and nucleus presented spherical shape and then gradually changed greatly.In spermatid,chromat in first condensed partly from exterior to interior and from top to basis, then condensed wholly into granules,into fibers and finally into homogeneous appearance;following the changes of chromatin nucleus decreased in size,the basal nucleu s membrane thickened and invaginated, followed with centriole transporting into t he fosse of invagination,and then nucleus gradually elongated and finally spired. Mitochondrion,symmetrically gathering at the rear of nucleus, amalgamated int o four blocks, elongated with the production of axoneme and spired too with the spire of nucleus.In the late stage of spermatid, some cytoplasm transported to the posterior of mitochondrion and formed the chamber of glycogen granule and then formed the sh eath of glycogen granules.Meanwhile the relict of cytoplasm removed out of cell and the spermatid was still covered with a layer of membrane relict. After membr ane relict disappeared,spermatid changed in to mature spermatozoon. Mature sperm atozoon was about 40μm in length,including a spiral head, a spiral middle piece and a nonspiral tail.The head,mainly composed of nucleus,had only one spiral bu ndle with seven spires.The middle piece,mainly constituted of mitochondria and a xoneme,had four spiral bundles of mitochondria.The tail was mainly composed of glycogen granules and axoneme with the “9+2” pattern.Between middle piece and t ail,there existed a interface with an annular. At the bottom of tail,g lycogen granules gradually decreased from two layers to one layer,and disappeare d finally. The spermatozoon of most gastropod had acrosome,but it couldn’t be observed in the whole spermatogenesis ofCipangopaludina chinensisGray.According to the v iewpoint of Franzen,that the functional need of fertilization determined the exi sting or not or the shape of acrosome,the spermatozoon ofCipangopaludina chinensis Gray perhaps had no acrosome.With spiral head and spiral middle piece,perhaps they could directly enter into eggs without the complex acrosome reac tion. In the stage of spermatid,noobvious microtubule occurred around nucleus,and the changes of nucleus were closely connected with the condensation of chroma tin. When chromatin condensed into granules nucleus decreased in size,and when chromatin condensed in fibers nucleus elongated.So the mechanism that determined the final shape of nucleus of the spermatozoon of Cipangopaludina chinensis Gray perhaps was related to the condensation of chromatin,but not the role of microtubule that was considered to be one of the mechanism of nucleus changing.But how chromat in could induce the nucleus spire was stil unclear and further studies should be taken to solve the problem.According to the classification of spermatozoon by Baccertti and Afzelius,the spermatozoon of Cipangopaludina chinensis Gray belonged to the modified type for the indistinct interface between head and middle piece or between middle piece and tail,for the elongating and spiring mitochondria,and for the sheath of glycogen granules.