TKN-S1MM:I) S'llCKI.EliACK 



6:)!) 



sometimes even the iircitcr nuuilier nt' ilicin iii.iy l)c 

 w.'iiitin^'. 'riie\' do not stand at riniit aniilcs tci tlic 

 hack, lull lean alterniitrK- towards the sides. They are 

 also set, not in a, straight line, hut in a /.\;s/->1'j: ('■'■' ■'■')■ 

 'I'hey are subnlate in form, somewhat cui-Ncd hui only 

 sli'>'liti\' widened at the base, with siiarp points and 

 smootii edges. In size tliey arc fairly ciiual. though ih<' 

 hindmost ra\- is generally sonicwlial laigci' than the 

 others" and eiiiial in length to the spinous ru\' in front 

 of the anal tin. All of these spinous ravs are usuallv 

 shorter than the diameter of the eyes; hut the anal 

 spine nia\' sometimes eijual this diameter in length. 

 Each ot them has a small, triangular tin-m<'udirane lie- 

 hind it. In this sjieeies too, the \entral sjiiues are the 

 largest, their length \arying between ', ,-, and ' , of the 

 distance between the first dorsal s])ine and the tip of 

 the snout. At the outer margins, at least in full-grown 

 specimens, they are usuallj' gi-aiiulated or even s|)iny 

 with osseous tubercles ari'anged in se\eral rows. Tlieir 

 articulations are constructed in the same manner as in 

 the preceding species. 



The pelvic bones are narrower than in the Three- 

 spined Stickleback, and the sinus in their anterior mar- 

 gin is deeper but narrower. Their uprigiit lateral jn'o- 

 cesses are somewhat broader and more obli(iuely cut at 

 the top. The interclavicles are also narrower than in 

 the preceding species, but of about the same length, 

 the pelvic bones lying entirely behind the ])erpendicular 

 from the insertion of the pectoral fins. 



The head as well as, in mo.st cases, the whole body 

 is more elongated (shallower) than in the Three-spined 

 Stickleback; but its relative length is about the same, 

 -being on an average about ^ ^ of that of the body. Its 

 structure is also the same as in the Three-spined Stickle- 

 back, with the exception of the character that lies in 



the abo\ I'-mentioneil arr.angenient of the branchiostegal 

 mendii'ant's. 



The soft-ra\-ed dorsal and the anal tins are also of 

 ;i low, triangular form. The first ray in each of them 

 is sim|ile hut distinctly ai-fieulafed. They arc fairly 

 analogous in |)osition, the beginning of the dorsal tin 

 never hiiiL;' in front of the perpendicular from the hind 

 part of the \cnt. 'l"he base of the s(jft-i-uyed dorsal tin 

 is alwa\s perceptibly shoi-ter than the head, but varies 

 between l'O and 24' \, ?0 of the length of the body. 

 The length of the base of the anal tin varies between 

 about If. and lit' ,_, ". of that of the body. 



The hind margin of the caudal tin is straight, some- 

 times slightly forked m- (nen convex, an indication of 

 the transition to (l((Mni-(i. Its length at the middle is 

 always perceptibly less than the jiostorbital length of 

 the head. The |)ectoi'al 'fins are similar To those of 

 tlie Three-spined Stickleback lioth in form and rela- 

 ive size. 



The internal (.irgans resemble those of the Three- 

 spined Stickleback; but the air-bladder is somewhat 

 narrower. Kroyek found some instances to corroborate 

 Cuviek's observation to the effect that the intestine runs 

 from the stomach straight to the vent, instead of pre- 

 viously forming a circular coil, as it generally does 

 both in this species and in the two pireceding ones. 



The relation between this species and the Three- 

 spined Stickleback is of especial interest when we con- 

 .sider the external differences of growth and sex, which 

 ■show that the Ten-sjjined Stickleback represents partly 

 the eai'lier (lower) stages of development and partly 

 the male characters. The following table of averages 

 contains the changes of growth most important in this 

 respect, together with the sexual differences especially 

 conspicuous in the Ten-spined Stickleback. 



Length of the body c.vpressed in HuUimctres 



Longitudinal diameter of the eyes in % of the length of the snout 



Postorbital length of the head in % of its total length 



Length of the base of the anal fin in % of the distance between the anal spine and the tip of the snout 



> > > head in % of the distance between the first dor.«al spine and the tip of the snout 



„ „ „ ., ., , „ „ anal 



Postorbital length of the head in % of the distance between the first dorsal spine and the tip of the snout 



Distance between the ventral spines and the anal spine \n % of the length of the head 



„ „ „ ,, ., ,, „ .. ,. „ „ „ „ distance between the ventral spines and the tip of the snout 



EksthOm (yet. Akad. Handl., 1. c), liowever, fomid tlic second \ay longest and tlie hindmost sliortest. 



