. The cell in development and inheritance. Cells. 140 THE GERM-CELLS connection with which, may be developed secondary or accessory fila- ments and other structures. At the tip the axial filament may lose its envelope and thus give rise to the so-called "end-piece" (Retzius). In Triton, for example (Fig. 66, F\ the envelope of the axial fila- ment ("principal filament") gives attachment to a remarkable fin-hke membrane, having a frilled or undulating free margin along which is developed a "mar- ginal ; Toward the tip of the tail the fin, and finally the e
. The cell in development and inheritance. Cells. 140 THE GERM-CELLS connection with which, may be developed secondary or accessory fila- ments and other structures. At the tip the axial filament may lose its envelope and thus give rise to the so-called "end-piece" (Retzius). In Triton, for example (Fig. 66, F\ the envelope of the axial fila- ment ("principal filament") gives attachment to a remarkable fin-hke membrane, having a frilled or undulating free margin along which is developed a "mar- ginal ; Toward the tip of the tail the fin, and finally the entire envelope, disappears, leaving only the axial filament to form the end- piece. After maceration the envelope shows a conspicuous cross-striation, which perhaps indicates a spiral structure such as occurs in the mam- mals. The marginal filament, on the other hand, breaks up into numerous parallel filDrilte, while the fila- ment remains unaltered (Bal- lowitz). A fin-membrane has also been observed in some insects and fishes, and has been as- serted to occur in mammals (man included). Later ob- servers have, however, failed to find the fin in mammals, and their observations indi- cate that the axial filament is merely surrounded by an envelope which sometimes shows traces of the same spiral arrangement as that which is so conspicuous in the connecting-piece. In the skate the tail has two fila- ments, both composed of parallel fibrillae, connected by a membrane and spirally twisted about each other; a. Fig. 68. — Spermatozoa of mammals, [.-/-i^from BALLOvvrrz.] A. Badger (living). B. The same after staining. C. Bat (Vesperugo). D. The same, flagellum and middle-piece or connecting-piece, showing end-knobs. E. Head of the spermatozoon of the bat (Rhino- lophus) showing details. F. Head of spermatozoon of the pig. G. Opossum (after staining). H. Double spermatozoa from the vas deferens of the opossum. /. Rat. head-cap (acrosome) ; k. end-knob; m. mid- dle-piece ;
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcells, bookyear1911
