THE THREE-SPINED STICKLEBACK 241 



Hemisphere, being recorded from as far north as 

 Greenland, Alaska, and Kamchatka, and ranging 

 southwards to Japan, California, New Jersey, and 

 Spain. 



The Three-spined Stickleback has the body com- 

 pressed and fusiform, with the head conical and 

 the caudal peduncle slender ; the mouth is small, 

 terminal, and oblique, and the jaws are furnished 

 with narrow bands of sharp teeth ; the gill-openings 

 are restricted to the sides. The dorsal fin is com- 

 posed of three, rarely two or four, spines, the two 

 first of which are free, and of nine to thirteen soft 

 rays ; the anal is similar to the soft dorsal, and has 

 one spine and seven to eleven soft rays ; each 

 pelvic fin consists of a spine similar to those on the 

 back, with a single soft ray in its axil, and is so 

 constructed that when everted it can be fixed by 

 means of an inner basal knob which catches against 

 the pelvic bone; the pectoral fins have a vertical 

 base, in front of which there is on each side a 

 glistening naked area bounded below by the bony 

 plates iectocoracoids) mentioned above as peculiar to 

 this group ; behind this pair of chest plates the 

 united pelvic bones appear, when seen from below, 

 as a lanceolate, triangular, heart-shaped or V-shaped 

 plate with the point directed backwards. 



There are no true scales, but on the sides of the 

 body a series of vertically expanded bony scutes is 

 variously developed, in some examples extending 

 from the head to the caudal fin, in others reduced 

 to three or four in the region of the pectoral fin. 

 The sixth plate (of the complete series) is usually 

 joined below to an ascending lateral process of the 

 pelvis, with which the fifth and seventh may also be 



