1881.] THE RABBIT AND HARE. 625 



two apertures as separate in the Rabbit ; but this is not the case, as 

 in the latter animal the ileum opens directly into the sacculus, and 

 there is thus only one common aperture into the colon (fig. iii, s.c) 

 The lips of this round aperture form the so-called ileo-colic valve ; 

 and its edge is often prolonged into a short process on one side. 



In other respects, with the exception of the number of turns of 

 the spiral valve, of which mention is made below, the caeca of these 

 two species present no important differences ; and the following de- 

 scription applies to both of them. 



The only other reference to this matter I have been able to find 

 is in a paper by Dr. Edwards Crisp, " On some Points relating to the 

 Habits and Anatomy of the Oceanic and of the Freshwater Ducks, 

 and also of the Hare (Lepus timidus) and of the Rabbit {L. cuniculus), 

 in relation to the Question of Hybridism" (Proc. Zool. Soc. 1861, 

 p. 82). In this paper, however. Dr. Crisp states that he has com- 

 pared the various viscera of these two animals, but has found no im- 

 portant difference in them. 



In the Piping Hare {Lagojnys jmsillus) there are two caeca, a large 

 and a small one. It seems probable that the latter is simply an 

 elongated sacculus rotundus '. 



Both the sacculus rotundus and the appendix vermiformis consist 

 internally of a mass of lymphoid tissue, abundantly supplied with 

 lymphatic vessels, each answering to an enormous Peyer's patch, and 

 having the ordinary structure^. Another Peyer's patch, averaging 

 about I of an inch in diameter, but varying much in size and shape, 

 occurs in the colon close to the aperture of the sacculus, on the side 

 which is furthest from the entrance of the ileum (figs. i. & iii. p^). 

 A much smaller one (fig. iii.^^) sometimes occurs on the other side ; 

 but this is very inconstant. 



A valve begins a short distance below the entrance of the ileum, 

 and makes about one turn {v"'), passing close above the ileo-colic 

 aperture, and is then either continued into the spiral valve of the 

 caecum {v^), as seen in fig. iii., or else ends off gradually, and the 

 spiral valve begins about | or | of an inch higher up (fig. i.). 

 This variation is seen in both species. 



Another valve, which is mentioned by Daubenton, and which Prof. 

 Huxley in his lectures speaks of as the intracolic valve (y^), begins 

 close to the sharp bend of the colon, and then makes one turn in a 

 spiral manner, ending off gradually, but being very large in the middle ; 

 it thus is capable of closing the way into the colon, and causing 

 the contents of the ileum to pass up the caecum. 



In the Rabbit the spiral valve makes 24 turns, not including the 

 part passing close above the ileo-colic aperture, which, as stated 

 above, is quite separate in many cases. In the Hare the number of 

 turns was 29 in the specimens I examined. 



The method I found to be most successful in making out the 

 structure and relations of these parts was, to carefully clean out the 



^ See Gegenbaui-'s ' Elements of Comp. Auat.,' English edition, p. 562, fig. 318 

 (after Pallas). 

 2 See fig. 1, p. 17, of the Harveian Oration 1873, by Dr. Eolleston, P.R.S. 



