22 SALMONID^ OF BRITAIN. 



than that of the body, but tine is marked by the orifice 



the lining membrane is puck- A/^Ki; °^ ^^^ chylopoetio duct (eh) 



ered with transverse folds ^SSf "while at the beginning of the 



thus increasing the extent of M ,S large intestine is a circular 



its secreting and absorbing iSSSv valve which is succeeded by 



surface, which is still further SFfM several others which are corn- 



assisted by the presence of hhIw f pletely or incompletely trans- 



csBcal appendages. The com- JPWB, «, verse (fig. 12). 



mencement of the small intes- 



Fig. 12. Cast of a part of the interior of the lower portion 

 of the intestinal tube in salmon showing the valves, v. 



It is curious to observe how, when some of these fishes select hard substances 

 for their diet, the coats of their stomachs, especially in its lower portion, may 

 become thickened, as in the gillaroo trout and other salmonoid forms. 



The ctecal* or pyloric appendages or pyloric cseca (pi/), already alluded to, 

 are secreting tubes closed at their outer end and situated at the commencement 

 and along the edge of the first part of the small intestines, where they begin in 

 three or four rows, which in the trout are gradually reduced to two, and finally 

 to one. Into these tubes food does not enter, but in the rich secretion which 

 flows from them it is very common in the salmon to find a species of tapeworm 

 (BothriocepTialus) . These pyloric csecaare generally considered as the representa- 

 tives of a modified pancreas in addition to the very rudimentary form of that 

 organ which opens into the small intestine in close proximity to the chylopoetic 

 duct (ch). 



The number of these csecaf are variable, fifty-one to seventy-seven having 

 been observed in the common salmon, and to differ largely in the various races of 

 trout as will be subsequently alluded to. They are capable of distension, of sub- 

 division, of amalgamation between two or more, and of being longer or shorter than 

 is ordinarily the case. The difficulty does not appear in discovering variation in 

 number, but in determining within what fixed limits they exist in a given 

 species. The eggs sent from the brook trout of Hampshire and Buckinghamshire, 

 by Mr. Frank Buckland and Mr. Francis Francis, to Tasmania, developed into a 

 large race in which these caeca seem to have normally reached fifty-two, showing 

 a considerable increase in number and proving such to be inconstant and 

 consequently of little if any value for the purpose of discriminating a species. 

 Marine species and varieties of Salmonidee appear to generally possess more of 

 these appendages than do the strictly fresh-water races,J as would also seem to 

 be the case in brook trout when transferred to a warmer clime. 



The urinary organs are composed of the kidneys as an excretory apparatus, 

 the ureters, the bladder, and the urethra. § 



These organs are distinctly separated anteriorly one from the other : they are 

 placed close to the vertebral column, but divided from the abdominal cavity and 

 the intestines by the air-bladder, and the peritoneum. 



Salmonides, in common with other teleostean or bony fishes, are dioecious, the 

 sexes being present in different individuals. In the male the reproductive organs 

 or the testes are symmetrica], distinct one from the other, placed beneath the 



* These appendages are more readily separated one from another and counted after they have 

 been a few hours- in alcohol ; while if first inflated with air by means of a blow pipe or with spirit 

 the cseca will be rendered more distinct. 



f Parnell, struck with the number of these oteca in the Loohleven trout, termed it Salmo 

 ctecifer. Dr. Gtinther considered of the number of pyloric appendages that " there can be no 

 doubt that this character may materially assist in fixing a species," and at page 11 ante, can 

 be seen the numbers he attributed to each form. 



% This is in accordance with what has been already stated (page 6), that casoal appendages are 

 more common in marine than in fresh-water fishes, and almost confined to such as have a marine 

 ancestry. 



§ The kidneys, according to Vogt and some others, appear to be composed of the Wolfian 

 bodies, structures persistent among fishes, but which are not permanent among other vertebrate 

 animals, whereas other authors deny this. The anterior portion or head contains no malpighian 

 bodies and was regarded by Balfour as a lymphatic glandi 



