INTESTINAL TRACT OF MAMMALS. 225 



convinced, however, that such vague resemblances between 

 Rodents and Artiodactyles are convergent. 



At its most dorsal extremity the recurrent limb of the pendant 

 loop sweeps round to be continued backwards as the rectum. 

 In Dipus and in many other Rodents the rectal portion is 

 relatively simple. It may be much lengthened, especially in its 

 proximal portion, and this lengthening may take the form of a 

 single rather narrow loop, an ansa coli sinistra, as for instance, 

 in Rystrix, or, as is more common, a much-contorted loop or 

 number of loops, as in Lagostomys and Dolichotis. I do not 

 attach much importance to this distinction, as I have found both 

 forms in different examples, both apparently adult, of Atherura^ 

 and in ver}^ young and adult examples of some other species. 



Variability appears to be a marked character of the subsidiary 

 loops of the hind-gut in Rodents. Three writers have given 

 a good deal of attention to the matter. Tullberg, with whose 

 work, unfortunately, I was unacquainted when I wrote in 1905, 

 published a most valuable monograph on the group (Tullberg 

 1899), in which a long section and many plates are devoted to 

 descriptions of the gut of a very large number of Rodents. 

 Tullberg devoted himself chiefly to the gut and its attachments 

 as seen in the unfolded condition when the abdominal cavity is 

 opened, but there are few features that cannot be understood 

 from his careful figures. My work followed in 1905, and later, 

 Dr. Beddard (Beddard, 1908), following the method of Tullberg, 

 I'ather than mine, called attention to a good many differences 

 that he had noted in examination of some of the species that 

 Tullberg had described, and added descriptions of the conditions 

 he found in other species not described by Tullberg. I have 

 tabulated the results of the three wi-iters. It Avould be a waste 

 of space to give the details; it is enough to say that the colic 

 loops of Rodents appear to differ individually and at different 

 stages of growth, in number, attachments, degree of spiral 

 coiling, relative length, and distinctness (i. e., definite narrowness,, 

 or width and minor expansions). I hesitate, therefore, to 

 follow Tullberg, even in his cautious use of these structures in 

 the classification of Rodents themselves, and I think it an 

 unwise adventure to pursue the comparison of the individual 

 loops from Rodents to other groups. With the reservation that 

 these colic loops are rather inconstant, it is possible to distinguish 

 them up to a, point. Immediately distad of the caecum lies what 

 Tullberg calls the paracsecal loop, corresponding with what I 

 have termed the postcsecal loop. This may be absent, imperfectly 

 formed, definite, nearly straight, twisted with the cfecum, or 

 showing an independent spiral. Next come the two loops of the 

 recurrent limb that are most commonly present in Rodents. 

 These are termed by Tullberg ansce de.vtrce 1 and 2. Frequently 

 only one is present, especially in young examples of a few days 

 old. Dr. Beddard, unfortunately, has confused the matter by 

 labelling the upper or more distal of these the ansa sinistra 

 Proc. Zool. Soc— 1916, No. XY. 15 



