首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Some of the senses that we and other terrestrial mammals take for granted are either reduced or absent in cetaceans or fail to f
Some of the senses that we and other terrestrial mammals take for granted are either reduced or absent in cetaceans or fail to f
admin
2011-02-05
40
问题
Some of the senses that we and other terrestrial mammals take for granted are either reduced or absent in cetaceans or fail to function well in water. For example, it appears from their brain structure that toothed species are unable to smell. Baleen species, on the other hand, appear to have some related brain structures but it is not known whether these are functional. It has been speculated that, as the blowholes evolved and migrated to the top of the head, the neural pathways serving sense of smell may have been nearly all sacrificed. Similarly, although at least some cetaceans have taste buds, the nerves serving these have degenerated or are rudimentary.
The sense of touch has sometimes been described as weak too, but this view is probably mistaken. Trainers of captive dolphins and small whales often remark on their animals’ responsiveness to being touched or rubbed, and both captive and free-ranging cetacean individuals of all species (particularly adults and calves, or members of the same subgroup) appear to make frequent contact. This contact may help to maintain order within a group, and stroking or touching are part of the courtship ritual in most species. The area around the blowhole is also particularly sensitive and captive animals often object strongly to being touched there.
The sense of vision is developed to different degrees in different species. Baleen species studied at close quarters underwater—specifically a grey whale calf in captivity for a year, and free-ranging right whales and humpback whales studied and filmed off Argentina and Hawaii—have obviously tracked objects with vision underwater, and they can apparently see moderately well both in water and in air. However, the position of the eyes so restricts the field of vision in baleen whales that they probably do not have stereoscopic vision.
On the other hand, the position of the eyes in most dolphins and porpoises suggests that they have stereoscopic vision forward and downward. Eye position in freshwater dolphins, which often swim on their side or upside down while feeding, suggests that what vision they have is stereoscopic forward and upward. By comparison, the bottlenose dolphin has extremely keen vision in water. Judging from the way it watches and tracks airborne flying fish, it can apparently see fairly well through the air-water interface as well. And although preliminary experimental evidence suggests that their in-air vision is poor, the accuracy with which dolphins leap high to take small fish out of a trainer’s hand provides anecdotal evidence to the contrary.
Such variation can no doubt be explained with reference to the habitats in which individual species have developed. For example, vision is obviously more useful to species inhabiting clear open waters than to those living in turbid rivers and flooded plains. The South American boutu and Chinese beiji, for instance, appear to have very limited vision, and the Indian sinus are blind, their eyes reduced to slits that probably allow them to sense only the direction and intensity of light.
Although the senses of taste and smell appear to have deteriorated, and vision in water appears to be uncertain, such weaknesses are more than compensated for by cetaceans’ well-developed acoustic sense. Most species are highly vocal, although they vary in the range of sounds they produce, and many forage for food using echolocation. Large baleen whales primarily use the lower frequencies and are often limited in their repertoire. Notable exceptions are the nearly song-like choruses of bowhead whales in summer and the complex, haunting utterances of the humpback whales. Toothed species in general employ more of the frequency spectrum, and produce a wider variety of sounds, than baleen species (though the sperm whale apparently produces a monotonous series of high-energy clicks and little else). Some of the more complicated sounds are clearly communicative, although what role they may play in the social life and ’culture’ of cetaceans has been more the subject of wild speculation than of solid science.
Which species swims upside down while eating?
选项
答案
freshwater dolphins
解析
(文章第四段提到Eye position in freshwater dolphins, which often swim on their side or upside down while feeding, 淡水豚在吃东西的时候经常是来回地游。)
转载请注明原文地址:https://jikaoti.com/ti/DKtMFFFM
本试题收录于:
B类竞赛(英语专业本科专科)题库大学生英语竞赛(NECCS)分类
0
B类竞赛(英语专业本科专科)
大学生英语竞赛(NECCS)
相关试题推荐
Robotsareusefulinexploringspacebecausetheycanworkintheconditionswhichexistinspace.Suchrobotsusuallylooklike
Haveyoueverthoughtaboutinventingsomething?Didyouworrythatyourideawastoostrangeorunrealistic?Well,maybeyoush
Makeasix-letterwordusingonlythesefourletters:
Livinginaforeigncountryisfun,butitisn’talwayseasy.Therearemanydifferencesbetweenculturesandalthoughsomeofth
Whenyourphoneisinyourpocket,therearetwopossiblestates:itiseithervibrating【D1】________.Meanwhile,youals
Livinginaforeigncountryisfun,butitisn’talwayseasy.Therearemanydifferencesbetweenculturesandalthoughsomeof
NewspapersandtelevisionreportsaroundtheworldshowAfricaasacontinentwithmanyproblems.Theyfocusonthewars,thest
Therewasapowercutthismorning.______,Icouldn’tdoanythingwithmycomputer.
WhyhasMarybeenabsentfromclass?
WhyhasMarybeenabsentfromclass?
随机试题
急性细菌性痢疾时,结肠溃疡的特点有()。
组织公关调查活动的第一个具体环节是()。
被告人邹某因涉嫌抢劫罪被人民检察院起诉,人民法院在审理该案过程中:如果邹某在法庭审理过程中从看守所脱逃,合议庭应当如何处理?()
成长能力主要体现在()。
某企业2011年实收资本为500万元,资本公积为400万元。该企业2010年资金账簿上已按规定贴印花2500元,税率万分之五。该企业2011年应纳印花税为()元。
Toimpressafutureemployer,oneshoulddressneatly,be______,anddisplayinterestinthejob.
在关系数据库中,把数据表示成二维表,每一个二维表称为【】。
对数据访问页与Access数据库的关系的描述错误的是()。
Theseaisthelargestunknownpartofourworld.Itcovers【B1】______percentoftheearth.Thereisstillmuchtobediscovered
A、Theweatherisverybad.B、Theyarelackinginmoney.C、Theydon’thaveenoughboats.D、Theoilishardtocleanupfromthes
最新回复
(
0
)