BIHANG TILL K. SV. VET.-AKAD. UANDL. BAND 28. AFD. IV. N:0 8. 39 



given may be satisfactory to show how the first start of the 

 development of a coecum has begun, so to say, and how the 

 way to further development became opened. The specializa- 

 tion of this first rudinient of a coecuni in the shape of a 

 slight excentric dilatation at the anterior end of the large 

 intestine, was of conrse eonnected with and dependent upon 

 the new functions to which it could be adapted and these 

 will be discussed låter on as far as the lizards are con- 

 cerned. 



"When I want to trace the first beginning of the coecum 

 to such a simple origin as the excentric dilatation of the with 

 food-material heavily charged large intestine, it is evident 

 that I admit that such a condition can have offered itself as 

 a possibility for further development several times indepen- 

 dently, in the lower vertebrate series, or, with other words, 

 that I regard the polyphyletic origin of a coecum as likely. 

 There is conseqnently, as far as I can see, no need to assume 

 any direct genetic connection between, or common origin for 

 snch groups of vertebrates that possess a coecum on account 

 of the presence of such an organ. When I hold such an opi- 

 nion, and as well in reptiles as in batrachians different stages 

 of development can be demonstrated from the simple excen- 

 tric dilatation of the large intestine to, at least in the former 

 a typical and fully differentiated coecum, I must decidedly 

 oppose against the by Gegenbaur^ maintained hypothesis 

 that the coecum has been derived from an organ which origi- 

 nally did not belong to the intestine (»der Darmwand ur- 

 sprtinglich fremd^, 1. c. p. 174). The proof that Gegexbaur 

 offers for this hypothesis is also exceedingiy unfortunately 

 chosen, when he describes the coecal tract of Igunna which 

 in fact is the most specialised — in consequence of the her- 

 bivorous diet of this lizard — as >.primitive» (»ein Anklang 

 an den primitiveren Zustand», 1. c. p. 173). The author quo- 



that the large intestine is suspended by the mesentery which is comparati- 

 vely less elastic than the wall of the intestine itself, and, especially anteri- 

 orly, is as a rule rather short. "When the large intestine is filled and heavy 

 the from the gravity resulting strålning must niore or less influence the strai- 

 ned organs, the mesentery and the intestine, and as the latter is the more 

 elastic one its shape must be somewhat altered and more or less oval in sec- 

 tion so that its dorsiventral diameter is prolonged. This might account for 

 the fact that often in batrachians and also in some lizards the excentric di- 

 latation of the intestine takes place in a dorsiventral direction. 



^ Vergleichende Anatomie der Wirbeltiere. Bd. II. Leipzig 1901. 



