290 ENULUTIUN AND MANKIND. 



remembered that there are moditications due to the possible 

 presence of food-yolk in the ovum, the acquisition of .special 

 larval characters, and other causes, all of which have to ha 

 considered in the scientific interpretation of the recapitulation 

 hj-pothesis. 



It may here be remarked that retrogresslim or dej^eneration 

 occurs in the animal kingdom, as is well shown in an embryo- 

 log-ical study of the Ascidia or sea-squirts, which, from a young 

 active tadpole-like stage, become sedeiUary and relativelv de- 

 generate. 



Distribution or Regional Grouping of animals also affords 

 evidence of evolution. It is well established that, while certain 

 animals have a wide range of distribution, others only occur on 

 very limited and often isolated areas of the earth's surface. This, 

 distribution can be explained on the hypothesis that the earth has 

 been populated by the descendants of common ancestors that 

 migrated ifrom place to place as occasion permitted, and under- 

 went modifications in various directions. The peculiar fauna of 

 certain parts of the world is proportional to the length of time and 

 the extent of the isolation of the special area from other areas. 

 Thus, Australia has been separated from Asia probably since the 

 Cretaceous period, and the numerous peculiar marsupials, such as 

 kangaroos, wombats, wallabies and phalangers are not yet sup- 

 planted by the more recently developed groups of animals. The 

 presence of Ornithorhynchns and Echidna, which belong to the 

 Monotremes, are living links with the past — their reptile-like 

 appearance, reptile habit of egg laying and mammalian habit of 

 suckling their young are O'bvious recapitulative features of ances- 

 try. In New Zealand, which is even more isolated than Australia, 

 wp. find no less peculiar inhabitants, including the remarkable 

 tuatara lizard [Sphenodon) and the kiwi bird (Aptcryx) which i- 

 about the size of a hen, and other flightless birds, some, such as 

 the Moas. recently extinct. These flightless birds have been 

 aptly described by the late Professor W. K. Parker as 



overgrown, dcsencrate birds that were once on tlic right road for 

 becoming flying fowl, but through greediness and idleness never reached the 

 goal — went hack, indeed, and lost their sternal keel, and almost lost their 

 unexercised wings. 



There are also the palacoaoological or fossil evidences of 

 evolution. Unfortunately, the bodies of many animals are un- 

 suitable for preservation as fossils, owing to the absence of hard 

 parts. Also, many layers of rocks have been broken or destroyed, 

 and only a small portion of those that remain can be examined. 

 However, throughout geological history, there has been continual 

 change in the types of animal life, gradually leading to those 

 existing at the present day. Occasionally it is possible to trace 

 fully the evolution of species from each other. This is well seen 

 among the Mollusca, as shown in the gradual transition between 

 Paludina neuniayri and P.hocrncsi. 



It is only possible to consider some of the vertebrates or 

 backboned animals, and certain of the forms that mav have griveii 



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