VISCERAL ANATOMY OF THE CHAEACINID^. 57 



Citharinus latus. — 16 cms. Intestine 80 cms. Ratio of intestine to fish 5 : 1. 



Distichodus niloticus. — 23 cms. Intestine 60 ( + ) eras. Ratio of intestine to fish 3 : 1 approximately. 

 Prochilodus lineatus. — 16 cms. Intestine 45 cms. Ratio of intestine to fish 3 : 1 nearly. 

 Xenocharax spilurus. — 16-7 cms. Intestine 28 cms. Ratio of intestine to fish 2 : 1 roughly ; or more 

 nearly, 5 : 3. 



In Ciir/matm dohiila the intestine forms a beautiful and evidently very long coil, 

 almost mathematical in the precision of its concentric circles, and constitutes a most 

 striking object when the body-cavity is opened, looking like a small coil of cord. But it 

 is so fine — ait any rate in the small specimens (8 cms.) on which my observations were 

 chiefly made — that I have not attempted measurement. 



As in the stomach, so in the length of the intestine, Xenocharax evidences a lower 

 stage of sj)ecialization for the herbivorous habit than either Cltharinm or Distichodus. In 

 this fish, moreover, the intestine does not exhibit the uniformity of calibre which 

 characterizes the Characinids generally. Thits, in the specimen on which my observation 

 was made, the first 16 cms. were narrow, the next 6 or 7 cms. rather wider, and the 

 terminal 5 or 6 cms. very wide, resembling a second stomach in caj)acity. This latter 

 condition was something more than mere distension due to enclosed material. In 

 Distichodus also I have noted similar but less marked variations : the intestine being 

 rather wide for 3 or 4 cms. ; then narrow, and fringed as above mentioned, for about 

 9 cms. ; then narrow and plain for some 10 or 12 cms. ; then apparently wider for a 

 long segment, which is intricately coiled ; the terminal 8 cms. the widest of all. For 

 Citharinus my notes are less precise, but here too I have recorded a variation of width in 

 different parts of the intestine, the terminal 5 cms. being the widest. In Prochilodus 

 the intestine was of uniform width, as also in Curimatus, so far as could be seen without 

 minute dissection. 



In these forms the intestine was found to be full of very fine soft mud, said to consist 

 largely of diatoms, though this I cannot assert from observation. The intestine is 

 thus of a dark brown colour. In Citharinus and Distichodus, possibly as a result of the 

 action of the spirit, the whole lining membrane of the body-cavity was infiltrated with 

 brown material which had apparently oozed through the intestinal wall. In a radiograph 

 of Citharinus, taken under my direction, a curious effect is observable, the intestine 

 having been rendered opaque to the rays by the mud contained in it. In the carnivorous 

 forms subjected to the same treatment nothing of the kind resulted. 



The Air-Bladder. 



The air-bladder in this family of fishes is well developed, and resembles externally that 

 of the Carps. It is constricted into anterior and posterior chambers, the cavities of which 

 remain in communication throus'h a narrow and extremely short tube. The bladder 

 lies immediately beneath the vertebral column, and extends usually from the diaphi-agm 

 to the posterior end of the body-cavity, where it often tapers to a point. It may, 

 however, be considerably shorter than the body-cavity ; and, on the contrary, in one 

 instance, to be referred to later, it is continued between the caudal muscles to the very 



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