STICKLEBACKS. 87 



reckoning the vertehrce in a specimen of the G. leiurus and in one of the 

 Irish sticklebacks of a simih\r length, I find that the number in the latter 

 exceeds that in the former species, and that they are throughout more 

 regularly equidistant than in the G. leiurus. 



In the three English sticklebacks, G. trachuriis, G. semiar mains, and 

 G. leiurus, the bony plate covering the head is much stronger than in the 

 Irish fish — the outline of the lower jaw more angular — the lips smaller 

 and less fleshy — the number of rays in the fins difierent, consisting gener- 

 ally, in the Irish specimens, of twelve in the dorsal, ten in the pectoral, 

 eight in the anal, and twelve in the caudal. In the three English Gas- 

 terosfei, also, the ventral spine is longer, but not so broad as in the Irish 

 fish — the dorsal spines considerably longer, and the plates whence they 

 spring proportionately larger. The following is the measurement of the 

 spines in the four S23ecies : — 



Total length offish. First dorsal spine. Second. Ventral. 

 G. trachurus . . 2 in. H lin. 2^ lin. 2|lin. 4 lin. 



G. semiarmatus .2 6" 2i 3 4* 



G. leiurus ... 2 6 2^-3 4| 



Irish species, • • ) q n 1 1 i ■! o i 



u. brachycentrus . . ) ■* 44 



In the last species * the membrane extends to the extremities of all the 

 spines. 



About Belfast I have taken the smooth-sided sticklebacks — G. leiurus 

 and G. brachycentrus — from ditches in the low grounds, from clear 

 mountain-streams at an elevation of 600 feet above the level of the sea, 

 from the muddy rivers Blackwater and Lagan, and from water which was 

 partially salt (here G. leiurus only), when, contrary to what might be ex- 

 pected, the largest were invariably found where the tem])erature was 

 lowest, specimens there [G. brachycentrus) not uncommonly attaining the 

 length of three inches, and perfectly free from the pearl-like tumours, 

 which, adhering to the body, infest those inhabiting the comparatively 

 warm waters of the lower grounds. This short-spined stickleback here 

 exhibits, in all respects, the same colours as the most common of the 

 English varieties ; of many of the larger individuals captured in the 

 month of September, about the one-half were red on the under parts. In 

 large shoals, too, I have remarked fully this pro])ortion to have assumed 

 the scarlet, and in the early summer months I have observed that full- 

 grown fishes, in which the most intense shade of this colour ])revailed, 

 never appear to be with spawn,+ very few in that state being so much as 

 faintly tinged with it. This Gasterosteus and the trout [Salnio Fario) 

 seem not to co-exist in some of our smaller rivers, or do so very partially. 

 In the stream whence the largest of these were taken, trout [Sahno Fario) 

 were a dozen years ago very common, and the stickleback unknown, and 

 it is only since the almost total disappearance of tlie trout tliat this fish 

 has been established in its waters. In a similar stream, issuing from the 

 same mountain-range, at about four miles distance, the trout yet main- 



* Agreeably to the view taken in the Hist, dcs Poiss., the term "species" 

 was here applied to G. brachycentrus. I was disposed at the time (1834) to re- 

 gard it as a local variety, but had not the means, which have since been aflbrdcd 

 by a comparison of specimens from numerous localities, to arrive at a certain 

 conclusion on the subject. 



t So late as the 19th Sept., 1832, I remarked one large with spawn. 



