MONSTIIOSITIKS. 277 



bitlcs uccasiuuiny souu" ik'K'tt'rit)iis i-11Vcf. Soiiioliincs the lowci- jaw is twistutl 

 round to one sitle, and may likewise be lengthened. 



Among single monsters the tail fin may be more or less horizontal like that 

 of a shrimp (plate xii, tig. o), or the body may bo curved so as to form a circle 

 round the yelk-sac (plate xii, iig. 12), or laterally (plate xii, lig. 1'.^). Or the 

 head may bo much developed Avhile the remainder of the body is rudimentary and 

 much resembles a tadpole. The head may be variously malformed. 



In some forms wo may observe distinct pathological changes in the spinal 

 column as has been observed by several authors as " The Hog-backed trout of 

 Plinlimmon," Camhriihje Quart. Mikj. 1833, p. 391 ; Cobbold, Edinh. Nno Phil. 

 Jour. ii. 1855, plate vi. In plate xii, lig. 12 is the (igure of a young 

 trout in which the spinal column is bent into an almost semi-circular 

 form and is of very great interest. It has been observed among the eggs 

 transmitted to long distances tliat there are always some alevins born with 

 spines curved into a more or less circular form. Attempting to swim 

 they go round like dancing dervishes and die on the absorption of the 

 yelk- sac. If, however, they are malformed to a lesser extent we find 

 spinal disease and a hunch-backed fish resulting. In 1747 Mr. Barrington 

 sent a paper to the Royal Society on the Hog-backed Trout of Flinlimmon. He 

 remarked that they occurred in watersheds wlicrc there were considerable falls, 

 and theoretically it seemed probable that suck might be occasioned by injuries 

 occurring to the embryo, and in 188G I tried what would be_ the effects of 

 concussion on eggs and their contents* (see p. 41 a^ite), and while the embryo 

 was still unhatciied : and assisted by Mr. S. Wethered, F.G.S., we ascertained that 

 concussion had occasioned spinal injury (plate xii, fig. 15). In accordance with 

 its extent the young fish has curvature of this portion of the body, and in the 

 slio-htest cases they recover but with shortening of the spinal column, occasioning 

 hog-backed deformity (plate xii, fig. 14). 



* The concussion of water falling from an elevation would act very similarly to the eggs being 

 dropped from a height and might occasion spinal irritation with subsetiuent disease and absorption 

 of the bodies of the vertebras thus reducing the length of the spinal column as figured, and, as is 

 also very commonly seen in members of the cod family, but in nature these are soon eaten up. 



