GASTEKOSTEUS AOULKATUS, ETC. 319 



great difference of their shape from that of their supposed 

 parent, more especially in the parts before the eyes, which, instead 

 of being elongated and slender, were short and round. In con- 

 .sequence of this, they were closely examined with glasses, and 

 drawn with the aid of a microscope of low power ; and, though 

 I failed to detect satisfactorily the ventral fins of that fish 

 (chiefly perhaps from their slender form and transparency), yet, 

 from the declivity of the head, protuberance of the belly, the 

 pectoral fin, and the length of the dorsal and anal fins, which 

 in some specimens were continuous with the caudal, and in others 

 separated hy a slight notch, I had no hesitation, in referring 

 them to the common Shanny." 



Now, the young of the Three-spined Stickleback differ just as 

 widely from the mature fish, as the young of the Fifteen-spined 

 species are stated to do ; and what is of still more importance 

 the differences are of exactly the same kind. In the former 

 (pi. iv., fig. 1 and 2) as well as in the latter, the parts before the 

 eyes are short and round, and can scarcely be said to project at 

 all in front ; the declivity of the head is consequently great ; the 

 belly is protuberant, and the dorsal and anal fins are long and 

 continuous with the caudal. The young of the Three-spined 

 Stickleback would therefore appear also to possess, at first, the 

 characters of the Shanny ; but as development goes on (pi. v., 

 fig. 1 and 2), the jaws are pushed out, the belly is reduced in 

 comparative size, and the dorsal and anal fins are shortened, and 

 become ultimately separated from the caudal. Thus, in course of 

 time, the young gradually assume the form and characters of the 

 parent. And there can be little doubt that this would have been 

 found to be the case with the young of the Fifteen-spined Stickle- 

 back, had Mr. Couch watched their development a little longer. 

 The obtuse form of the head, on which that gentleman places 

 much stress, is the embryonic condition of all fishes ; the elonga- 

 tion of the jaws is always an after -development. 



In conclusion, it may be remarked, that of the three or four 

 other species of fish, described to nidify, one, a native of Demerara, 

 is stated to remain by the side of the nest with as much solicitude 

 as the hen guards her eggs ; the same is said respecting another 



VOL. II. PT. III. 2 s 



