The right kidney is variable in position in reference to the left. In all species the right kidney lies anterior to the left but in some, _D. deserti_ and _D. ingens_, it is markedly anterior. In _Dipodomys agilis_, _D. merriami_ and _D. deserti_ there are small to large patches of lymphoid tissue on the caecum. These patches were not noted in any of the other species examined and I do not know their function. In the three above mentioned species, however, the large intestine is shorter in proportion to the small intestine than in any other species except _D. heermanni_ (see Table 2) and with the exception of _D. heermanni_, _D. venustus_ and _D. ordii_ the actual measurements are less. Inasmuch as little is known of the food habits of the various species of kangaroo rats, any ascription of adaptive significance to the varying proportions of the digestive system would be only speculative. Midgley (1938) describes the visceral anatomy of _D. ordii_ and _D. microps_. Except for the differences here noted the description of the viscera as given by Midgley (_loc. cit._) applies to the rest of the species studied. TABLE 2 VISCERAL MEASUREMENTS (in Millimeters) of DIPODOMYS ================================================================= Column Headings: H: heermanni M: merriami A: agilis D: deserti O: ordii S: spectabilis V: venustus P: panamintinus I: ingens H M A D O S V P I ----------------------------------------------------------------- Large intestine 432 290 464 397 237 413 374 419 430 Small intestine 165 126 220 195 131 228 207 255 274 Percent of small to large intestine 38.2 43.4 47.5 49.2 55.2 55.3 55.4 60.9 63.7 ----------------------------------------------------------------- From the differences noted in the skeleton, in the entire visceral mass, and in the shape and position of the liver it appears that as a saltator becomes more specialized skeletally, there is a concurrent compacting and aligning of the viscera into a more or less bilaterally balanced mass. It seems that this alignment is for a stabilization in leaping. It seems reasonable that the individual that has a loose and unconsolidated visceral mass, or in which the viscera or at least the heaviest part of the viscera is relatively unilateral, would be thrown slightly off balance at the end of the jump. This would place the animal at a slight disadvantage before being able to make the next jump. Howell (1944:40) comments on the fact that kangaroo rats often land off balance, "owing apparently to clumsy use of the tail." Possibly the unilaterality of the visceral mass plus a shorter tail and a more clumsy use of that organ accounts for the off balance landings which Howell has observed.