. The cell in development and inheritance. Cells. 142 THE No less remaikahk' is tlic ooniugation ul" spermatozoa in pairs (Fig. 68. //), which takes place in tlie vas deferens in the opossum (Sclcnka) and in some insects (Hallowitz. Auerbach). Hallowitz's researches ("95) on the double spermatozoa of beetles {Dvh'seufce) prove that the union is not primary, but is the result of an actual conjugation of previously separate spermatozoa. Not merely two. but three or more spermatozoa may thus unite to form a '• ;' which swims like a single spermatozoon. W
. The cell in development and inheritance. Cells. 142 THE No less remaikahk' is tlic ooniugation ul" spermatozoa in pairs (Fig. 68. //), which takes place in tlie vas deferens in the opossum (Sclcnka) and in some insects (Hallowitz. Auerbach). Hallowitz's researches ("95) on the double spermatozoa of beetles {Dvh'seufce) prove that the union is not primary, but is the result of an actual conjugation of previously separate spermatozoa. Not merely two. but three or more spermatozoa may thus unite to form a '• ;' which swims like a single spermatozoon. Whether the spermatozoa of such a group separate before fertilization is unknown: but Ballowitz has found the groups, after copulation, in the female receptacuUim. and he believes that they may enter the egg in this form. The physiological meaning of the process is unknown. 2. OtJicr Forms of Spcruiatozoa The principal deviations from the flagellate type of spermatozoon occur among the arthropods and nematodes (Fig. 69). In many of these forms the spermatozoa have no flagellum, and in some cases they are actively amoeboid ; for example, in the daphnid Polyplicuins (Fig. 69, A, B, C) as described by Leydig and Zacharias. More commonly they are motionless like the ovum. In the chilognathous myriapods the spermatozoon has sometimes the form of a bi-convex lens {Po/y- dcsj/ius), sometimes the form of a hat or helmet having a double brim (////ns). In the latter case the nucleus is a solid disc at the base of the hat. In many decapod Crustacea the spermatozoon consists of a cylindrical or conical body from one end of which radiate a num- ber of stiff spine-like processes. The nucleus lies near the base. In none of these cases has the centrosome been identified. ira ^ B Fig. 70 JEFF.] A. Mother- stage, with spe matozoid (the known as matozoon. ated than. 3. Paternal Gcnn-cclls of Platits In most of the flowering plants the male germ-cells are represented by two "generative nucle
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1906
