826 



SCAXDIX AVIAN FISHES. 



THRISSOMOKPHI. 



I'lii/scsfdiiis icitli the sliimlder-i/irdle suspended from the head (as usual in tlie Teleosts). Seapular disk Inter- 



iiidlji streiii/theiied Inj an (irch formed hi/ a special liane {os jjra-'oraenidenm) from the coracoid hone to the claricle 



The frst four ahdominal rertehra: of normal form and derelopment. Hyomandilndar and pteryfjopalatine archei 



complete, as irell as {in most eases) the operealar ajijiaraliis. MaxiUartj hones fullii dereloped. 



That Tlie Salmons and Hen'ings have much in 

 common, was declared l)y Agassiz in 184M", when he 

 united them iiitti one I'amil}-, Halecoides; and Cope 

 followed up this opinion in ISTl' by the establishment 

 of the order Isospondyli, answering to the series of the 

 Thrissoinorphs, and distinguished from the preceding 

 series mainly by a negative eliaracter, the absence of 

 tlie so-called acoustic bones. The connexion between 

 the organs of hearing and the air-bladder, however, is 

 not foreign to this series. In tlie Clujieoids Weber' 

 discoverefl that the aii-bladder, which tapers forward 

 for some length, is divided in front into two branches, 

 one to the right and one to the left, which pass through 

 the occipital bone into the cranium, and there, as Hasse'' 

 has shown, touch with their tips the (juter wall of tlie 

 lymphatic chamber surrounding the auditory apparatus. 

 .Sace.mehl has given good reason'' for his assumption 

 tliat this mode of communication is the more primitive, 

 from which the UKjre complicated connexion of the 

 preceding series has been evolved, and which has been 

 persistent not only in the Clupeoids and some other 

 Physostoms, but also in some Physoclysts of ancient 

 type, as for instance the Berycoids (cf. aliove, p. (3G), 

 the Macruroids, some Gadoids and Balistoids. We have 

 also seen a reminiscence of this connexion in the two 

 tubular processes which ascend from the anterior ex- 

 tremity of the air-bladder of the Gadoids (cf. above, 

 ]). 470) in vermicular curves towards the head, one 

 on each side of the anterior renal mass. The absence 

 of the so-called acoustic bones is thus explained as an 



■hes 



earlier stage of development; and a negative character 

 of this signiiicatioii can hardly be sufficient to deline 

 a natural evolutionary series. \\'c also find that a great 

 number of tlie Thrissomorphs are witJKjut the character 

 adduced by Agassiz as one of the most important in 

 his definition of Halecoides, namely the jiarticipation 

 of the maxillai'v bones in the formation of the margin 

 of the upper jaw. Thus we might reasonably treat 

 these forms as a distinct series of families {Scopelo- 

 morphi): but the resemblances in otiier respects are 

 sufficientlv great to render the Tlirissomorphs a natural 

 whole, with the same limitations as Cope's Isospondyli, 

 although the said resemblances do not constitute cha- 

 ractei's applicable to the whole series. Within this 

 series too the variation of form and structure is great 

 and affects most of the organs. Scales and a distinct 

 lateral line ma}' l)e present or ^vanting. The maxil- 

 laries may be simple, as in the I'est of the Teleosts, 

 or composite, furnished with so-called supplementary 

 bones answering to the cheek-bones {ossa jiiiialia) of 

 the higher vertebrates. The teeth may be numerous 

 and well developed or wanting. A so-called adipose 

 iin is present on the hind part of the liack in many 

 forms, but wanting in others. Luminous organs, so- 

 called phosphorescent spots, may lie present or absent. 

 The ovaries may be furnished with an oviduct or with- 

 out a complete tube of this description. The air-bladder 

 mav be present or wanting. Such great differences in 

 forms which nevertheless sho\v their natural affinity 

 in some wa^• or other', render the chai'acterization ot 



" Reck. Poiss. Foss., tmii. V, pp. 3 ami !)l). 



' Iclit!i>/ol. Less. Ant, Tnins. Anier. Philos. Srjc. Pliilad. X. ser., vol. XIV, pp. 452 and 454. 



" De mire cett., p. 73, cett.; figg. 03, celt. 



'' Anat. Stud., Bd. I, p. 599, cell. 



•■ Morphol. .Jahrb., Bd. X, p. 51. 



' Thus for example tlie llaplorjutoiilil.n — a family of fresh-water fishes from South America and Australia — are almost typical 

 Salmons, lint have tlie margin of the upper jaw formed by the intermaxillaries nlone; and similarly the Sternopti/cliiila' and ScpeluUv are 

 families so like each other that they ought hardly fo be kept .apart, though in the former the osseous framework of the mouth follows the 

 Halecoid type, while the latter preserve in this respect the ordinary Teleosteous character. 



