STICKLKliACKS. 



tl45 



spinous j.iroccsscs of two \ertclii'a', tlic ])Ost('rior (jii 

 llidsc (if I'diu'. Tims we have us a rule to deal witli 

 S iiitoi'spiiiMl plates at the dorsal wlgc in tVuiit of the 

 sott-rayed dorsal fin. In one single case, however, 

 Heincke could trace 9 of these interspinal plates, the 

 last two each with a distinct, well-developed spinous 

 ray, and tlie tliird, t'ounfinii' from l)eliind, witii a ru- 



Fig. 159. Ga.ilerosleiis aculeiitn.'i. traclninis. Natural size. From 



the Frisches Haff, off Konigsberg. — ~' tlie posterior, detached part 



of the tliiril (lor.^al plate (<is. J). After Heincke. 



diineiitary spinous ray "in tlie form of a rigid spine." 

 The Three-spined Sticklehack has thus shown at least 

 traces of as many as 5 free spinous rays at the dor- 

 sal edge. 



If we now observe the arrangement of these 5 

 spinous rays, we shall find that each one of the 9 



c/s4 //sf. 



Fig. 160. Gaslerostcu.< nculeatus, trachurus, leiracanthiis, with the 



supernumerary spinous ray set on the penultimate dorsal plate. Natural 



size. From Kiel Bay. — " the posterior, detached part of the fourth 



dorsnl plate (df. 4). After Heincke. 



dorsal plates, witii the exception of the tirst, may be 

 furnished with a spiiujus ray, though not simultaneously. 

 In order to ex])ress the differences that occur in this 

 respect, we shall denote each of the interspinal plates 

 by an Arabic figure (1 — !)), the plates which in each 

 case must be regarded as double, by brackets ( — — ), 

 the three ordinai-v spinous rays by the Roman num- 



erals I — III, tlie most usual supcfntniicrar\' ray by IV, 

 and till- rudimentary and superniiTnerary ray that has 

 only once been ol)ser\ed, by \ . The cases (varieties) 

 observed h\ IIki.nckk are then as follows: 



..■1; in Three-spincd Sticklebacks with 'A free spinous rays at 

 the dorsal edge. 



a: with the regular number (fi) of interspinal plates, the 

 forms most typical in this respect (figs. 157 .and 158). 



I II III 

 \ — -> — o"^^ _,5_J^_0 — « — 9 



h: witli 7 interspinal plates (the 3rd and 4tb detached 

 from eacli other, (ig. 159). 



(I 10 II III 



1 2 — 3 — 4 — h^ i; — _ 8 — 9 



^,, 





- '^i^^liiSiaf— -^?, '-^^ 



Fig. 161. Gasterosteus aculeatii.t, trachuvus, tetracanthus, with the 



supernumerary spinous ray set on the penultimate dorsal plate. 



Natural size. From Eckernforde Bay. After Heincke. 



B: in Three-spined .Sticklebacks with 4 free spinous rays at 

 the dorsal edge. 



(■; with a supernumerary spinous ray on the penultimate 

 interspinal plate, otherwise as in variety «. 36 speci- 

 mens out of (il showed this arrangement (fig. 161). 

 I_ _IJ_ IV III 



1^2—3^4—5—6—0—8—9 

 (/; similar to c, but with the 5th and 6th plates detached 

 from each other (liir- 1(!0). 16 specimens out of 61. 



(I I ^ II IV III 



1 _ 2 — 3^^ _5_(5_()_8 — 9 



e: with a supernumerary spinous ray on the 6th plate and 

 with this plate detached from the 5th. 4 specimens 

 out of 61. 



I II IV III 



1 __ 2 — 3^ 4 — 5-6-0 — 8-9 



/; with only 5 interspinal plates, otherwise similar to c. 

 i specimens out of 61. 



1 II IV III 



— 2 — 3^^ — 5^^6 -- — S — 9 

 ij: with only 6 interspinal plates, otherwise as in d. 1 

 specimen out of 61. 



I 11 IV III 



— 2 — ~— 4 — 5 — 6 — 0-8 — 9 

 h: with a supernumerary spinous ray on the 4th inter- 

 spinal iilato. which is detached from the 3rd, the latter, 



