380 Mr. J. Higginbottom on the British Tritons. 



of August there is a visible diminution of the number in that 

 element. I have seen some as late as the middle of August, and 

 but rarely in the beginning of September. 



In the middle of August I have procured a number of both 

 species from crevices and embankments, whither they have re- 

 tired until the next breeding season. 



VI. Peculiarities in the Anatomy of the Triton. 



In the tadpole state the Triton is furnished with no less than 

 four distinct organs for respiration: 1st, the gills; 2nd, the 

 branchial fringes ; 3rd, the lungs ; 4th, the cutaneous surface 

 and expanded tail and crests. 



The gills form three perfectly distinct semilunar arches im- 

 mediately beneath the operculum on each side. 



The branchial fringes extend and float externally so as to admit 

 of the circulation being readily observed under the microscope, 

 and each loop is continued along one of the semicircles of the gills. 



In addition to these forms of respiratoiy organs, the lungs 

 are visible on opening the general thoracico-abdominal cavity. 

 These contain air from their earliest period. It is obvious that 

 the lung will answer the purpose of the air-bladder in fishes. I 

 have repeatedly observed that the tadpole is at one time of rather 

 less specific gravity than water, rising to and remaining at the 

 surface without efi'oi't, and at other times of rather greater spe- 

 cific gravity than that fluid, falling to the bottom of the vessel in 

 the same manner. 



I scarcely need make any observation on the cutaneous sur- 

 face as a respiratory organ. 



The blood circulating in the expanded tail and crests is almost 

 as much exposed to the respiratory medium as that in the bran- 

 chial fringes themselves. 



As the period for quitting the water approaches, the branchial 

 fringes disappear and the opercula closely adhere over the gills, 

 which also disappear in their turn. 



The other peculiarities of the anatomy of the Triton relate to 

 its resumption of the water, and to its new function of reproduc- 

 tion at the spring of the fourth and subsequent years. The 

 crest in both species of the Triton, and the fringe or mem- 

 brane in the posterior extremities of the Triton Icevis, undergo a 

 rapid development in the months of February and March. They 

 are obviously destined to enable the animal to move about rapidly 

 in its native element and assist in aquatic respiration (PI. XVI. 

 fig. 5). 



In the month of June these adjuncts begin to disappear, and 

 by the middle of July the crest, &c. remain only in the form of 

 mere ridges (PI. XVI. figs. 6 & 7). 



