Arthur. — On the Brown Trout introduced into Otago. 509 



Our heavier still rivers do not appear, with their grand stock of smelts 

 and whitebait, etc., to cause any increase in the number of the pyloric caeca, 

 over those of trout in our rougher and poorer streams. This I have proved 

 from a careful examination of a fair number of specimens. And, it is also 

 curious, that a sea-trout caught in Sawyer's Bay, which I opened, had only 

 40 caeca, while it must have had the finest possible range of feeding 

 ground. 



What I have now said regarding these organs in our trout amounts to 

 this: — The actual number of caeca observed in Otago is greater than 

 Giinther's recorded number of them at Home ; but the evidence I have 

 adduced shows that this increase in number is not owing to an additional 

 demand on the caeca to work, necessitated by the presence of more food, 

 but in all probability to a difference in age of the fish examined. Or, more 

 plainly, there has really been no alteration in the number of the pyloric 

 casca, or in the extent of their absorbing surface. 



There remain but one or two observations which I have to make on 

 structure before finishing my paper, which has expanded into dimensions I 

 did not anticipate, so much so that I may have to reduce the appendix I 

 thought of, if I do not omit it altogether. The first is, that in nearly every 

 female with developed ovaries the left lobe is much longer than the right 

 lobe. And, as to the theory of the thickness of coating in stomachs of 

 trout, (as the G-illaroo trout of Ireland), being a consequence of the food 

 being shellfish, this I must say — that most of our rivers contain a wonderful 

 number of the previously mentioned Limvum, an active little mollusc, which 

 I have found in our trouts' stomachs in incredible numbers. At the same 

 time there are parts of some rivers where they are absent, and where of 

 course the trout cannot get them to eat. I have not paid particular 

 attention to the action of any food on trouts' stomachs as yet; at the 

 same time, had there been any difference between those of trout from 

 either feeding grounds, it is probable that I should have noticed it. And, 

 I certainly have not seen either a thickening or hardening of the walls of 

 the stomach.* 



Remarks on Variations. 



1. The first variation is a decided one in the spawning season, being 

 two months later, and the duration of hatching a fortnight longer, than in 

 England. But what may be the cause of this I cannot explain. 



* Since writing above, I have found this shellfish at the head of the stomach, and 

 near the vent in great intestine of a one-pound trout from Waipahi River, and in both 

 cases the living animal was digested out of the shells, while these were not broken or 

 affected in any other way. 



