颊窝毒蛇的毒牙是长的空心管子.The fangs of pit vipers are long, hollow tubes.只有四分之一的蛇具有毒液和毒牙.Venom and fangs are found in only a quarter of all known snakes.在蛇的进化史上,毒牙的出现是新的进步.A more recent advance in the evolutionary story of snakes i...
Many nuclei have become shrunken and dark and have then undergone karorrhexis ( fragmentation ) and karyolysis ( dissolution ).许多细胞核发生了核浓缩,接着出现核碎裂和核溶解现象....