爬行纲的主要特征 (1)皮肤干燥,缺少腺体;表皮角质化,外被角质鳞片或盾片。 (2)五趾型的附肢及带骨进一步发达和完善,指趾端具角质爪。 (3)骨骼骨化程度较高,硬骨的比重增大。头骨具单一枕髁,有颞窝形成。脊柱分化明显。 (4)体内受精,发育无变态,产羊膜卵

鱼纲的主要特征: 1.无颈部,体多呈纺锤形,并常覆有保护性的鳞片; 2.终生生活于水中,以鳃呼吸; 3不仅有奇鳍,而且有偶鳍,偶鳍不超过2对,偶鳍肢带不与脊柱发生联系; 4.有发达的上下颌,多数种类的颌上有锐齿;

哺乳纲的主要特征 1.有高度发达的神经系统和感觉器官 2.出现了口腔消化 3.体温恒定 4.具有陆上快速运动的能力 5.胎生、哺乳,完善了陆上繁殖的能力

1.脊索动物门的主要特征: （1)出现了脊索 （2)具中空的神经管 （3)出现了咽鳃裂 （4)肛后尾 （5)脊索动物的心脏及主动脉

Department of Electrical Engineering and Computer Science 6.003: Signals and Systems-Fall 2003 LIVE Tuesday, October 14, 2003 Directions: The exam consists of 5 problems on pages 2 to 19 and work space on pages 20 and

REMINDER: Quiz 1 will be held from 7: 30 to 9: 30 p. m. Tuesday, October 14 The quiz will cover material in Chapters 1-3 of o&w Lectures and Recitations through september 26, Problem Sets 1-3 and that part of Problem Set 4 involving problems from Chapter 3 Reading assignments

then, assuming we choose wM