354 Stapley and Leivis : 



of the forms below them in the scale of evolution," the I'ecession 

 of the caecum from a longer type is established. Those who 

 deny that the appendix is a vestige of a larger ancestral caecum 

 have the weight of embryological evidence again them. 



Heisler's emibryology says: — "In the third month the 

 appendix has already acquired the form of a slender curved tube 

 projecting from the caecum. At the time of its first appearance 

 and for some weeks later the apjjendix has the same caliber as 

 the caecum. Subsequently the caecum outstrips the appendix in 

 growth, the latter appearing in the adult stage as a relatively 

 very small tube attached to a much larger caecum." 



The claim that is made that the aj^pendix is a development 

 and not a recession is I'efuted by a macroscopic study of the 

 anatomical types of caecum, by a study of the embryology of 

 the appendix and caecum, and by studying the lines of force that 

 go to determine the appendicular shape. Upon such lines it 

 is quite easy to follow during atrophic processes the formation 

 of the vermiform appendix, but it is not possible to understand 

 the development of an appendix. The vermiform appendix can- 

 not be developed. It can only be formed during recession of the 

 caecum. Development cannot occur because development im- 

 plies "an increased caecal content, and an increased caecal content 

 exerts its force against the fundus of the caecum and not against 

 the appendix. (Fig. 13). 



Leaving the subject of caecal changes in man, we will deal 

 with caecal changes in the only order besides primates that has 

 an animal which shows a true vermiform ajopendix — the mar- 

 supial. Outside primates, ttie only animal that has an appendix 

 is the wombat. (Figs. 1-7.) There are many points of strong 

 resemblance between the wombat and the koala (Fig. 19), for 

 it is highly probable that at an early date they were closely 

 related. The koala took to the gum trees and lived exclusively 

 on gum leaves; the wombat took to the ground and lived on 

 roots and other food less bulky and more nutritious. The his- 

 tory of this change of food is to be seen in the caecum of these 

 animals. The koala has an enormous caecum to digest its gum 

 leaves, the wombat has only a vermiform appendix to represent 

 its caecimi; otherwise the digestive tracts of the wombat and 

 the koala are alike. The Victorian wombat (Phascolomys 



