DARWIN MEMORIAL CELEBRATION 
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Illustrations 
1. Mammalian limbs adapted for use in various ways, though they 
exhibit the same kind of skeletal framework. 
2. Specimens illustrating the different forms of leaves of the ferns 
and their relatives. 
V K 
PRINCIPLES OF EMBRYOLOGY 
When an animal develops, it passes gradually from its early stages with 
their simple construction to the progressively complex stages of later and 
adult life. During this process, it closely resembles in an embryonic condi¬ 
tion an adult organism of a lower order. The general principle of develop¬ 
ment is that an embryonic series of stages exhibited by any animal is a 
brief review or recapitulation of the ancestral history of its kind. 
Illustrations 
1. Models and specimens displaying the gill-slits of chick embryos, 
and their correspondence with the gill-slits of fishes. 
2. Models showing the blood-vessels and the hearts of different 
classes of vertebrates, and some of the corresponding embryonic 
stages in the development of the heart in man. 
3. Preparations showing the occurrence in a chick embryo of a 
primitive body-support, the notochord, which occurs in the 
adult in Amphioxus, -a primitive relative of the vertebrates, 
and in vertebrates. 
4. Models showing the development of the human brain, and its 
resemblance at various stages to the adult brains of lower 
mammalia. 
5. The third eye or pineal body of an adult lizard, and the corre¬ 
sponding vestige in the embryonic human brain. 
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RUDIMENTARY AND VESTIGIAL ORGANS 
Vestigial organs are remnants of once-useful parts, that have undergone 
regressive evolution. Rudimentary structures often occur in some forms, 
while in related species they reach a far higher degree of development. 
