620 



SCANDINAVIAN I-ISIIICS. 



as broad and cxininded like ;i wiiii:. I>iir the hi aiicliio- 

 stegal lueinbranes ai-c entirely hidden under the eoininon 

 dermal covering, so that tlie Arlediaii character of the 

 order iiolds good as an external one. The pelvic hones 

 are genei'aliy wanting, hut soinetiines ])resetit, as in tiie 

 Balistoids, in which case they are united into a large, 

 scythe-shaped hone, inf'eriorly hounding and supporting 

 the abdominal ca\ it\-, even when the pectoral fins have 

 disappeared or have been reduced to a spiny, osseous 

 ])rojection at the hind extremity of this bone. The 

 remaiiid(!r of the skeleton is marked not only I))" its 

 weak ossification, l)ut als(j by the small number of the 

 vertebra', which may sometimes (in the Coffer-fishes) 

 sink to 14 and never exceeds 30. Sometimes, as in the 

 Tetrodonts, the upper spinous processes (neural spines) 

 of the first o or 6 vertebra are longitudinally cleft in 

 two, with the halves laterally extended. Ribs are want- 

 ing in most cases, but present in the Balistoids. As 

 the caudal fin is frequently of extraordinary size — though 

 with few, less than 13, branched rays — , its insertion 

 in the skeleton has also undergone proportionate increase 

 in strength and firmness, i)artly by means of large 

 h)-pural bones, which are firmly united in the Coft'er- 



])osttemporal and mastoid bones, and the same length 

 of the pelvic bones, which in the Acanthuroids, however, 

 are not confluent. Set side Ijy side with the skeleton of 

 an AcfiiifliKiKs the skeleton of a liallstes seems at tlie 

 first glance to claim a position within the same famih'. 

 The systematic separation between tiie Plectognates and 

 the other Physsoclysts is thus by no means too great to 

 admit of their lieing ranged side by side with each other. 

 .\bout 200 species of Plectognates are known. The 

 greatest wealth of forms belongs to the tropical seas; 

 but one or t^vo species penetrate into rivers, or even 

 pass their Avhole life there. To man these fishes are of 

 only slight \alue. Their flesh is in general not eaten', 

 and many of them are even poisonous. They attract 

 attention, however, both by their extraordinary form 

 and often by their beauty of colour, as well as by their 

 singular maimer of life, ^lost of them are shore-fishes, 

 but some belong to the surface-regions of the ocean; 

 they do not include any deep-sea forms of pronounced 

 character, although two species have been met with 

 below the 100-fathoms line'. Most of them are ren- 

 dered incapal)le of anv \igorous motion by their hard 

 and stiff dermal covering or by their clumsy form. 



fishes into a compressed tip, hard as ivory, partly by | By the small size of the gape most of them are com- 



high and longitudinally extended, neural and haemal 

 spines on the last caudal vertebrte. Sometimes however, 

 as in the Sunfishes, the caudal fin is a secondary growth 

 and finds an extremely feeble suji^iort in the more or 

 less atrophied tip of the tail. 



In spite of tlie considerable differences that occur 

 both in the form and covering and also in the internal 

 structure, the Plectognates together form a natural group, 

 Avith persistent traces of the Ganoid type, which give 

 them an appearance unusual in the fauna of our day. 

 The nearest apjiroach to the ])receding forms we find, 

 as Cope has already pointed out", in a comparison Ije- 

 tween the Balistoids (especially the genus Trincantlius, 

 with its free maxillaries) and the Leather-fishes (Acan- 

 thuridce, a family within the lomjirehensive series of 

 Mackerel-fishes), with the same form of body, the same 

 elongation and deepening of the forepart of the head 

 and shortening of the jawbones, the same union of the 



pelled to find subsistence in small animals or in pieces 

 torn from larger ones. Their food consists chiefly of 

 corallines, jellv-flshes, worms, or mollusks. The lively 

 colours that adorn many of them are reminiscences of 

 their life in the coral-groves, where they associate with 

 scaly-finned Cluvtodonts of no less varied hues, or among 

 the seaweeds with their shifting colours. The species of 

 ])lainer dress resemble the sand in colour, or are attired 

 for a life in the open sea.. Their powerful teeth may 

 well serve to ]irotect them from attack, but as a rule 

 they have ([uite otlier weapons of defence. MauA' of 

 them have been famed from ancient times for their 

 faculty of filling the oesophagus, which is capable of 

 extraordinary distension, with air. In this manner the 

 bod}' is expanded, sometimes to a perfect globe, and 

 the dermal spines are erected in all directions into a 

 front of pointed spikes. "One day," wrote Darwin from 

 Bahia in 1832'', "I was amused by watching the habits 



° Trans. Amer. Philos. Soc, Philad., vol. XIV, n. ser., p. 458. 



' According to Sohlegei. (Sike., Fn. Japan.), Lowever, several of these fishes are eaten by the Japanese: one Tetrodon is even stated 

 to compose the principal food of the poorer classes (luring winter, while the fisherman is forbidden, under pain of heavy penalties, to expose 

 for sale other species of the same genus. 



' Bofli these finds, however (see GOnther, Deep Hea Fi.ih. Chall. En-peel., p. 26(i). "lav liave entered the (rnwl while it was being- 

 sunk or hauled in. 



■* A Natiifali.<i)' Voi/nge (London, ed. 1884) p. l.T. 



