192 



DR. P. CHALMERS MITCHELL ON THE 



Dr. Bedclarcl compared it with the pendant loop of mammalian 

 embryology, and was so fortunate as to find a remnant of the 

 umbilical cord passing to the apex of this loop. I have never 

 found this structure in any full-grown marsupial, and think that 

 Dr. Beddard's example was an individual peculiarity ; but it is 

 interesting to note that it occurred precisely at the position in 

 which I always look for it, and its jiresence confirms the validity 

 of text-fig. 1 A as a diagram of the primitive mammalian gut- 

 pattern. 



Text- figure 5. 



Intestinal tract of Thylachms cynoceplialus. 

 Description as in text-fig. 4. 



The polyprotodont marsupials display gut-patterns of great 

 simplicity. In some {Bidelpliys, Peragale) the condition is 

 practically identical with text-fig. 1 B (Mitchell, 1905). In 

 others, such as those described above, a condition of greater 

 simplicity has been reached, due to the obliteration of the 

 distinction between the regions and the loss of the ctecum. This 

 simplicity is to be regarded as secondary, as, otherwise, it would 

 be necessary to suppose that the distinction into definite regions 

 and the presence of a definitely placed ctecum had been acquired 

 independently in many different groups. 



