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infectious diseases, new surgical techniques for saving human lives, or new treatments for spinal cord injuries without the use of animals. Even so, most
scientists favor what are now called the three Rs : (1) replacement of animals by in vitro, or test-tube, methods whenever possible; (2) reduction of the
number of animals used in experiments; and (3) refinement of experiments to cause less suffering to animals.
F. Barbara Orlans of the Kennedy Institute of Ethics at Georgetown University says, It is possible to be both pro research and pro reform. She
feels that animal activists need to accept that sometimes animal research is beneficial to humans, and all scientists need to consider the ethical dilemmas
that arise when animals are used for laboratory research. Do you approve of this compromise?
Understanding the Terms
acoelomate" 308
amphibian" 323
annelid" 315
anthropoid" 328
arachnid" 317
arthropod" 316
australopithecine" 330
bilateral symmetry" 308
bipedalism" 329
bird" 324
bivalve" 314
bony fishes" 322
Cambrian explosion" 307
cartilaginous fishes" 322
cephalization" 308
cephalopod" 314
chitin" 316
chordate" 320
cnidarian" 310
coelom" 308
Cro-Magnon" 332
crustacean" 316
culture" 330
deuterostome" 313
echinoderm" 319
ectothermic" 324
endoskeleton" 307
endothermic" 325
exoskeleton" 307
filter feeder" 310
flatworm" 311
gastropod" 314
hermaphrodite" 312
hominid" 329
Homo erectus" 330
Homo habilis" 330
Homo sapiens" 331
insect" 318
jawless fishes" 322
lancelet" 320
leech" 315
lineage" 328
lobe-finned fishes" 323
lung" 323
mammal" 326
marsupial" 326
molting" 316
monotreme" 326
mosaic evolution" 330
multiregional continuity
" hypothesis" 331
Neandertal" 332
nematocyst" 311
nephridium" 315
notochord" 320
out-of-Africa hypothesis" 331
placental mammal" 327
planarian" 311
prosimian" 328
protostome" 313
pseudocoelom" 308
radial symmetry" 308
ray-finned fishes" 322
reptile" 324
roundworm" 312
segmentation" 309
sponge" 310
tunicate" 320
vertebrate" 320
Match the terms to these definitions:
a. _______________ Localization of the brain and sensory organs at the anterior end of an animal.
b. _______________ Body cavity enclosed by mesoderm.
c. _______________ Possesses both male and female sex organs.
d. _______________ Longitudinal cut through the body at any point gives two equal halves.
e. _______________ Generate internal heat.
Arboreal
Both a gull, which flies in the air, and a penguin, which doesn t, are birds.
Both a cat and a duckbill platypus, which has a bill like a duck, are mammals.
Check Your Progress
1. Compare and contrast nutrition in animals with nutrition
in fungi.
2.
Compare and contrast nutrition in animals with nutrition
in plants.
Answers:" 1. Both animals and fungi are chemoheterotrophs. Fungi digest their food externally, while animals digest their food internally." 2. Animals are
chemoheterotrophs, while plants are photosynthesizers.
Figure 19.2" Sea life in the Cambrian period.
The animals depicted here are found as fossils in the Burgess Shale, a formation in the Rocky Mountains of British Columbia. Some lineages represented by these
animals are still evolving today; others have become extinct.
Figure 19.4" Radial versus bilateral symmetry.
a. With radial symmetry, two mirror images are obtained no matter how the animal is sliced longitudinally. Radially symmetrical animals tend to stay in one place and
reach out in all directions to get their food. b. With bilateral symmetry, mirror images are obtained only if the animal is sliced down the middle. Bilaterally symmetrical
animals tend to actively go after their food.
Figure 19.5" Type of body cavity.
a. Flatworms don t have a body cavity; they are acoelomates, and mesoderm fills the space between ectoderm and endoderm.
b. Roundworms are pseudocoelomates; they have a body cavity, and mesoderm lies next to the ectoderm but not the endoderm. c. Other animals are coelomates, and
mesoderm lines the entire body cavity.
Figure 19.6" Proposed evolutionary tree of animals.
This proposed evolutionary tree is based on RNA sequence data. Compared to the traditional tree, many more phyla are considered protostomes and they are divided
into two unique groups. The annelids (segmented worms, such as the earthworm) are placed in one group, and the arthropods are placed in another, even though both
are segmented animals.
Figure 19.3" Evolution of animals.
All animals are believed to be descended from a type of protist; however, sponges may have evolved from a protist separately from the rest of the animals.
Figure 19.9" More
cnidarians.
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