344 TH^ EVOLUTION OF MAN. 



this becomes very large, while in those which eat flesh it 

 remains very small, or is entirely aborted. In Man, as in 

 most Apes, the beginning of the blind intestine alone 

 becomes wide ; its blind end remains very narrow, and 

 afterwards appears only as a useless appendage of the 

 former. This " vermal appendage *' is interesting in dys- 

 teleology as a rudimentary organ. Its only importance in 

 Man consists in the fact that now and then a raisin-stone, 

 or some other hard, indigestible particle of food becomes 

 lodged in its narrow cavity, causing inflammation and 

 suppuration, and, consequently, killing individuab other- 

 wise perfectly healthy. In our plant-eating ancestors this 

 rudimentary organ was larger, and was of physiological 

 value. 



Finally, w© must mention another important appendage 

 of the intestinal tube; this is the urinary bladder (uro- 

 eystis) with the urinary tube (urethra), which in develop- 

 ment and in morphological character belong to the intestinal 

 system. These urinary organs, which act as receptacles and 

 excretory passages for the urine secreted by the kidneys, 

 originate from the inner part of the allantois-stalk. The 

 allantois develops, as a sac-like protuberance, from the 

 anterior wall of the last section of the intestine (Fig. 286, u). 

 In the Dipneusta and Amphibia, in which this blind-sac 

 first appears, it remains within the body-cavity (coeloma), 

 and acts entirely as a urinary bladder. In aU Amniota, on 

 the other hand, it protrudes considerably out of the body- 

 cavity of i^e embryo, and forms the large embryonic 

 " primitive urinary sac," which, in higher Mammals, forms 

 the placenta. At birth this is lost ; but the long allantois- 

 stalk (r) remains, its upper portion forming the central navel 



