DARWIN MEMORIAL CELEBRATION 
9 
parent in different characteristics. Sometimes the hybrid offspring will 
exhibit “reversion,” that is, it will differ from both its parents, and will 
resemble a remote ancestral form. The laws of inheritance have been 
much more adequately formulated since the time of Darwin, as in the case 
of Mendelian inheritance. 
Illustrations 
1. Specimens of hybrid plants together with their parents. 
2. Examples of hybrid fowls. 
3. The Darwinian instance of reversion in fowls. 
4. The results of hybridization in mammalia. 
G 
THE FOSSIL RECORD 
Following the identification by geologists of the relatively old and the 
relatively recent layers of rocks, the remains of animals and plants of earlier 
ages of the earth demonstrate the occurrence at first of simpler organisms, 
and the successive appearance of more and more complex groups. Some¬ 
times the fossils constitute a comparatively complete series of ancestral 
species leading to modern kinds, as in the Horse and many invertebrates. 
Illustrations 
1. A series of specimens of fossil plants showing the succession of 
their appearance upon the earth. 
2. The general succession of invertebrate groups. 
3. The evolution of cephalopodous mollusks,— Nautiloid and 
Ammonitoid types. 
4. The evolution of several snail or gasteropod types: 
a) Fulgur series. 
b) Fusus series. 
c ) Paludina series. 
5. The evolution of Lamp-Shells, or Brachiopods, as exemplified by 
Spirifer mucronatus . 
6. Specimens of fossil-bearing rocks showing unmodified and meta¬ 
morphosed conditions. In the latter case the fossils are 
destroyed. 
7. The evolution of the Horse. 
8. The evolution of the Camel. 
