40 INTESTINE AND DIET OF REPTILES. 



ted has also, as is already mentioned, erroneouslj'- interpreted 

 tlie iijjper diapliragmatic valve of the colon of Iguana as 

 forming a part of the wall of that peciiliar, specific organ 

 which secondary has become connected with the intestine 

 and trausformed to a coecum. This is done for the purpose 

 of showing that in several lizards a »schärfere Sonderung 

 (of the coecum) vora Enddarm» is to be found. But such an 

 assumption can hardly serve the purpose. The arrangement 

 of valves etc. in the coeco-colic tract of /^ita>*ais one of theper- 

 fectly secondary adaptations in the intestinal canal of this 

 lizard to its diet. »Die fingerförmige Driise am Enddarm 

 der Selachier» which Gegenbaur regards as the homologue 

 of the coecum may have a somewhat corresponding situation 

 to that of the coecum of the lizards both being organs con- 

 nected with the large intestine and in consequence hereof as 

 HowES^ has shown, the bloodsupply is furnished b}^ correspon- 

 ding arteries. But the direct homology of the digitiform 

 appendix of the plagiostome fishes and the coecum of the li- 

 zards can not be admitted to be proved by this, the only 

 thing proved by the mode of vascularisation is that both 

 organs in question belong to the large intestine, but nothing 

 more. For every new or old specialization from the same 

 part of the large intestine must receive its bloodsupply from 

 the same source as its matrix, the intestine itself. The ho- 

 mology of the matrix is however not the same as the homo- 

 logy of the secondarily from the same matrix derived new 

 organs or structures. Therefore if the ancestors of the pla- 

 giostome fishes have had a diverticle from that part of the 

 intestinal canal which corresponds to the large intestine of 

 the lizards and other higher vertebrates, and this diverticle 

 låter become transformed into the digitiform appendix of the 

 now living sharks and rays, it does not follow that this ap- 

 pendix shall be homologous to the coecum of the lizards and 

 other higher vertebrates- although the latter organ also is 

 derived from the large intestine. The study of the intesti- 

 nal canal of the lizards offers another example of the deve- 

 lopment of a diverticle from the intestine in a situation 

 where also many fishes have similar diverticles. It has been 



^ Journ. Lin. Soc. Vol. XXIII. 



^ It seems to me very questionable whether the douLle cceca of birds are 

 quite homologous with the simple coecum of the lizards. 



