ICHTHYOLOGY. 



227 



ClassiBca- families, to reduce them to an uniform nomenclature, and 

 tion — Der- some groups that have been recently characterized have 

 mopteri. jjggj, introduced. 



CLASS OF FISHES. 



Order I.— DERMOPTEROUS FISHES. 



Sub-Order L— PHARYNGOBRANCHS. 

 This order is named from the c\itaneous vertical fins, in 

 which the mucoid rays are extremely soft and delicate, or 

 altogether imperceptible, and from the want of pectoral 

 or ventral members. The first two sub-orders are founded 

 on the different developments of the respiratory organs. 

 In the first the pharynx itself is organized for respiration, 

 and two processes having the function of gills project 

 freely into the cavity of the mouth; tlie water necessary 

 for respiration flowing over them by the same canal which 

 carries the food ; there being no lateral gill-openings 

 through the skin. Of this sub-order the best known 

 representative is the Amphioxus lanceolafiis of Yarrell 

 {Branchiostoma lubricum, Costa), which was first made 

 known to the world as a Limax or Slug by Pallas, who 

 received it from the Cornish coast. Recently Mr Couch 

 rediscovered it on the same shores, and Mr Yarrell has 

 described it in his excellent work on British Fishes, ac- 

 cording to its true affinities as a fish, though its want of 

 a head was puzzling. Its structure has since been in- 

 vestigated by Ratke, Johannes Miiller, Owen, Goodsir, 

 Swan, and other first-rate comparative anatomists, — many 

 specimens having been procured among the gravel and 

 rocks of the sea-beaches in the south of England, also in 

 the Irish Channel, on the Norway coast, and in the Medi- 

 terranean. The longitudinal slit forming the orifice of its 

 mouth, resembles, to the unassisted eye, that of a Lamprey, 

 its jointed labial feelers looking like moveable teeth. It is 

 a thin semi-transparent creature about an inch and a half 

 long, without jaws, but having a large buccal cavity into 

 which the short vascular processes that perform the function 

 of giUs project freely, without cartilaginous supports or 

 lateral attachments. The buccal cavity communicates 

 by a small pharyngeal opening with a wide barrel-shaped 

 oesophagus, which occupies more than a fourth of the whole 

 length of the fish, and whose interior surface is ciliated 

 throughout, and organized to assist in respiration. Vessels 

 that ramify over its vertical ciliated bands communicate 

 with the dorsal and ventral portions of the vascular trunk 

 that carries on the circulation, without the intervention of 

 a central propelling organ. There is, however, beneath 

 the posterior end of the expanded oesophagus a small 

 widening of the circumferential vessel which pulsates 

 rythmically, and which Professor Owen considers to be a 

 rudimental representation of the branchial heart of the 

 Myxinoids, the next order of fishes in point of organization. 

 The peculiarity of shape which distinguishes the Lancelet 

 from all other fishes, arises from all its nerves of the senses 

 devolving from the myelon or spinal marrow, without the 

 production of a ganglionic brain, and consequently, without 

 the necessary expansion of the protecting integuments 

 which make the head, and in animals more advanced in the 

 scale, provide sockets for the sense capsules. The only 

 cartilaginous part of this fish is a jointed haemal arch which 

 extends from the anterior end of the spinal chord on the 

 ventral aspect to the orifice of the pharynx, and serves to 

 support the oral filaments. It represents the labial arch of 

 the higher Myxinoids. Though this little creature wants 

 jaws, it has, as we have just mentioned, a large buccal cavity 

 which, as in other fishes, admits not only food, but also 

 aerated water, to the respiratory organs, and an enormous 

 oesophagus having the double function of deglutition and 



respiration. The intestine proceeding from the oesophageal Classifica- 

 bag is slender, almost straight, and terminates at the anus, ''O" — D^''- 

 about one-fourth of the whole length of the fish from the moptsri. 

 point of its tail. In its motions, the Lancelet is lively and "^"^^v~^ 

 active, and shelters itself quickly from observation among the 

 gravel. In 1853 Sundevall distinguislied two American spe- 

 cies of Amphioxus or Branchiosloma, the B.carilxfum from 

 the West Indies, and elongatutn from Peru ; but Professor 

 Peters on comparing the species found that caribteum was 

 identical with the European one. Dr Gray has described 

 a Borneo specimen as a distinct species, so that the genus 

 probably is not so poor in species as was at first supposed. 



CLASS.— PISCES. 



Order I.— DERMOPTERI. 



V^ermiform, abrachial and apodal ; endo-skeleton unossified; exo- 

 skeleton and vertical fins rauco-derraoid ; no pancreas; noair-bladder. 



The devolopment of the skull in the Dermopterous fishes is ar- 

 rested at more or less embryonic stages, but in each genus it pro- 

 ceeds in a specific direction ; thus, in the Lancelet, evolving an 

 articulated labial arch and its numerous filaments ; and in the 

 Myxinoids and Lampreys forming a more complex system of lateral 

 and labial cartilages ; or modifying the palatine, maxillary, and 

 hyoid rudiments in relation to the suctorial function of the mouth. 

 The olfactory organ, which is double in all other fishes, is single 

 in this order; and the eye is rudimentary, being merely a small 

 fold of skin coated with a speck of dark pigment. It is probable 

 that this point is sensitive to light, as the lowest member of the 

 order, the Lancelet, quickly secludes itself among gravel when ex- 

 posed to light. In Ammoc(vtea and the Myxinoides the cartila- 

 ginous capsules of the acoustic organs retain the embryonic posi- 

 tion of projecting spheres at the base of the cranium ; these are 

 less prominent in the Lampreys; in the Plagiostomes they are 

 imbedded in the walls of the cartilaginous skull; and in the bony 

 fishes they are walled up by ossification. The oral filaments and 

 soft integuments of the anterior end of the Lancelet and Myxines 

 receive many nervous twigs from the fifth pair ; and touch seems to 

 be the most important sense in these low vertebrals. 



Sob-Order L— PHARYNGOBRANCHII. 



Cirrhoetomi, aliorum. Gills free, pharyngeal ; no heart. A 

 single genus of few species. 



Family I.— AMPHI0XIDJ3. 



Genus I. Amphioxus, Yarrell. {Branchiosloma, Owen.) Re- 

 spiratory processes projecting from above the pharynx into the 

 large cavity of the mouth. Interior mucous coat of the widely 

 dilated oesophagus organized for aerating the blood. Mouth eden- 

 tate, furnished with exterior labial barbels. 



Sub-Obder II.— suckers. 



Genus Heptatrema, Dum. {Bdellostoma, Miill. Act. 

 Berol, 1838.) A single species is known, the Petro- 

 wyzou cirrhalus of Forster, who discovered it in Queen 

 Charlotte's Sound, on Cook's second voyage. It has since re- 

 ceived the appellations of Heptatreiiius Dombeyi and Bdel- 

 lostoma Forsteri. It is a lively, active fish, inhabits rocky 

 bottoms, lies in wait for fishes on which to prey, and was 

 frequently taken by our voyagers adhering to pieces of fish 

 which had been let down into the sea as bait. It has the 

 power of emitting an immense quantity of mucus from all 

 parts of its skin. The New Zealanders roast and eat it. 



Myxine, Linn. (Gasferobranchiis, Bloch.) The species 

 best known, Myxine glulinosa, Linn., or Glutinous Hag, 

 was classed by Linnaeus with the Vermes. The mouth 

 is a membranous ring, with a single tooth on its superior 

 part ; while the strong teeth of the tongue are arranged 

 in two rows on each side, so as to give to these animals the 

 appearance of having lateral jaws, hke insects or Nereides ; 

 but their tongue performs the office of a piston in exhaust- 

 ing the mouth so as to enable them to adhere to other 



