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2006-11-24 4:50 am
鯊魚的皮膚非常粗糙,佈滿許多齒狀突起(盾鱗),是由一個髓腔上覆象牙質構成,外面再包一層琺瑯質。盾鱗的形狀因種類而異,也是分類的依據之一。大多數種類的盾鱗是連續鋪排的。隨著年齡增長,盾鱗會脫落,新的盾鱗會跟著變大。盾鱗的是順著身體方向排列,並吸附一層水膜,以減少水流阻力。一般來說,母鯊的皮膚比雄鯊來得厚。以全身重量比例來看,有些鯊魚腦部的重量和鳥類或哺乳類差不多。
骨骼全為軟骨構成。在身體兩側,頭的後方各長有5-7個鰓裂,但是缺乏鰓蓋,所以鯊魚必須不停游泳,讓水通過鰓裂,不然會窒息而死。有的鯊魚則在眼睛後方長有呼吸孔(鰓孔),水會由孔流入,再由鰓裂排出。鬚鮫吸入海水後,會將嘴閉上,由嘴部肌肉和食道壁的收縮,使水流向腮裂。當鯊魚的嘴張開時,鰓裂會閉上,嘴關閉時則鰓裂打開。
鯊魚的腸子裡有一個相當特別的螺旋瓣,這是一種增加吸收面積的構造。這是由於鯊魚的腸子比一般脊椎動物都要來得短(與體長的比例為1:1)而演變出的結構,而螺旋瓣的形狀會因鯊魚的種類而異,螺旋的數目則多達45轉。螺旋瓣的構造都依據迴旋斜面、或在纏緊時形成大圈套住小圈的螺旋圈的原理,讓食物通過來進行消化。

回答 (1)

2006-11-25 11:03 pm
✔ 最佳答案
Because cover ivory of 髄腔上 of a unit of Yuichi that skin of a shark is very crude, and a lot of much dentation of cloth sticks out (a scale of a shield) does a hock of constitution, 瑯 of one level of 琺 wraps quality in the surface again. Thus form of a scale of a shield is different for a kind, and it is one of the grounds to classify equally. A scale of a shield of most kinds lays a line continually. A year and a scale of a rising shield can come off, and a scale of a new shield can obey that I change size. By it attracts a membrane of one level of water together, and reducing current drag by a thing of a scale of a shield freezes along a physical direction, and standing in line. Skin of a saying female goby generally stands out than a male goby and is thick. 或哺乳類 of birds is not very different from weight of little shark brains part if I watch weight proportion from head to foot.
All sake cartilage of a frame constitutes it. Freeze on physical both sides, and can tear gills of a unit of 5-7 of each head existence of a continuance of an edge, and correct it, and is deficient in gills with a cover, and a shark of a reason should swim in a thing of nonstop operation, and let split in water by gills; is different, and what learn suffocate, and thus die. When a certain shark does it, I freeze, and water society reason hole flows into a hole (a hole of gills) of long existence breathing of a continuance of eyes and can deal because gills can tear it again. A shark of 鬚 inhales seawater afterward, and a meeting does it over mouth closedown and lets a current split in cheeks from the shrinkage of a wall of an oral region muscle and the gullet. When a mouth of a shark opens, gills are split and learn it and close the top and close what a mouth can tear gills of 時則 and breaks.
One village existence of the bowels of a shark falls under a spiral valve especially, and this 是一 winds up that it increases structure to breathe an area. This is what the bowels which moved to a shark all than a general vertebrate stand out, and short を demands; (assume it long proportion of a body and 1): When thus the structure that gave that 1 develops into in) it, a kind for a shark of a-shaped meeting of a thus spiral valve are different, and do a spiral number; only as for nothing 45 rounds per minute reach it. I pass that I digest the principle that the particularly small spiral that I surrounded and structure of a spiral valve depends on 旋斜面 of 全部迴 or to wear a big crafty design of the hard formation surrounded for the food which can stop. .


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