INTESTINAL TRACT OF MAMMALS. 211 



large niiaor loops with ;i very short straight rectum. Although 

 the primitive mesentery saspeudiug the whole length of the 

 intestinal tract is continuous, a stroug secondary connection 

 forming a cavo-duodenal ligament attaches the proximal part of 

 the colou to the duodenal region, and has to be severed before 

 the gut can be laid out to display its pattern. The inner dorsal 

 wall of the CBeaum displayeil a median fold, running along the 

 dorsal wall somewhat in the fashion of tlie typhlosole of the 

 earthworm. It is conceivable that this may indicate an original 

 paired condition. In the case of these very simple patterns, it 

 is rather easy to see resemblances which may have little signi- 

 ficance, but it is undoubtedly notable that the pattern of the 

 Proboscidean gut in no way suggests that of the true Ungulates, 

 4i,nd very strongly recalls that of the Sirenia (Mitchell, 1905, 

 Hg. 15). 



Order Oetacea. 



Sub-Order Mystacoceti. Balimioptera physalus (text- 

 % 15). 



By the kindness of Mr. J. Erik Hamilton, I have had the 

 oppoi'tiinity of dissecting a young embryo of the Common 

 Rorqual {Balceiioptera phijsalus) taken from an adult captured 

 at Belmullet, Ireland. The duodenal region (text-fig. 15) is not 

 sharply separated from Meckel's tract. The latter is of even 

 calibre, and is thrown into a very large number of short, regu- 

 larly disposed minor loops suspended at the periphery of a much 

 elongated oval expanse of mesentery. These loops extend to the 

 extremity of the ti-act, and just where the recurrent limb of the 

 usual pendant loop begins its straight course towards the duo- 

 denal region, there lies n single small caecum. The hind-gut 

 consists of the almost straight recurrent limb, a short transverse 

 colon very close to the duodenum, but so far as I could make out, 

 suspended at this point only by the primitive mesentery, and of 

 n rather long nearly straight rectum. 



The crecum is short, but rather wide ; its cavity is continuous 

 with that of the hind-gut, and separated by a simple semi-lunar 

 ila,p from the entrance of the ileum. 



I have already described and figured the gut-pattern of one of 

 the Odontoceti (Mitchell, 1905, fig. 17). The Toothed Whales 

 have no caecum, antl the whole length of the gut, from the 

 stomach to the anus, is suspended on a straight dorso-ventral 

 mesentery, all of it, except a very short rectum, being tlu'ovvn 

 into closely-set minor loops. I ventured on the opinion, howevei", 

 that this almost i-eptiHan simplicity was not primitive, a.nd, 

 judging from the description given by Flower (1872, p. 428), I 

 suggested that the gut-pattern of Whalebone Whales would 

 approximate more closely to the common mammalian tj^pe. This 

 is actually the case. The characteristic mammalian pattern 



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