4i6 ELEMENTS OF BIOLOGY 



The island of Krakatoa between Java and Sumatra is now in 

 the process of developing a fauna and doubtless will in time con- 

 stitute an illustration of the effects of isolation and ensuing evo- 

 lutionary changes. The island was partially sunk by a volcanic 

 eruption in 1883, the area remaining above water being completely 

 denuded of all life by hot lava and ashes. This catastrophe is used 

 by Jules Verne as the climax adventure in one of his books. Three 

 years later plant life was found on the island. Six years later a 

 number of varieties of animals were found there, mostly insects. 

 Twenty-five years later, in addition to insects, snails, lizards, and 

 birds, were found. In 1920 there were more than 500 species of ani- 

 mals present, including bats and rats. These now constitute an iso- 

 lated group; future additions will be casual. The hereditary possi- 

 bilities of the group are contained in the germ plasm of these 

 early arrivals, and their descendants may be expected to demon- 

 strate descent with change from the original group, that is, 

 evolution. In January, 1933, Krakatoa was again in mild volcanic 

 eruption. Thus the isolated community of living forms is being 

 subjected to the environmental changes that have been the common 

 experience of life since its very beginnings. Such events have had 

 profound influence in the distribution and survival of living organ- 

 isms on all land areas. 



Evidence from Histology and Physiology. The several 

 tissues from various groups of animals present a uniformity of 

 appearance under the microscope that is unmistakable. Thus the 

 contractile tissues, striated muscles, of insects resemble the striated 

 muscles of mammals; distinguishing between microscopic prepa- 

 rations of muscles from various mammals is very difficult except 

 to a highly trained observer. In medico-legal cases the positive 

 identification of blood as human blood is possible only by intricate 

 chemical tests. Furthermore, certain cellular structures that appear 

 in Protozoa as specializations appear with modifications throughout 

 the entire animal series. The Sarcodina move by means of temporary 



