FISHES. 



A fish in the popular senge of the word is a member of any one of the 

 four classes of aquatic or fish like vertebrates, the Pisces (True Fishes), the 

 Elasmobranchii (Sharks, Skates, etc.), the Marsipobranehii (Lampreys), an,d 

 Lep'ocardii (Lancelets). A fish in this comprehensive and rather in- 

 definite sense may be defined as a cold- blooded vertebrate, adapted for life . 

 in the water, breathing by means of gills, the limbs if present developed 

 a fias, the fingers and toes being represented by cartilaginous rays con- 

 nectbu by membrane, the exoskeleton obsolete or developed as scales or 

 bony plates, and one or more fins developed on the median line of the 

 body, usually composed of rays connected by membrane. 



Of a fish, in the popular sense, one could hardly say more, without the 

 necessity of the constant introduction of exceptions. Of a "true fish, i.e., 

 a member of the Class Piscjy, a definition will be given further on. 



Of the four classes of fish- like vertebrates only tv/o are represented in 

 the waters of Ohio. These are the L'a.m-preyB {Marsip .bmnchii) and the 

 True Fishes (Pi-sees'). These two may be compartd as follows : 



* Skull iiaperfectly developed, without lo-wer jaw or membi are bores (operoula, etc.); 

 paired fins (pectorals and ventrals) nndeveloped, -with no shouk^er girdle or pelvic 

 elements ; gills puise-shape, nsually -with several external opening^-. ; nostril single, on 

 the median line of the head ; body ecl-^haped, scaleless. . . . Maesip'obranchii. 



**Skull well-developed, -with a loY'f jaw and membrane bones; paired fins more or 

 less devek'peu, wiih a shoulder girdle (i^rifjrm or furcala- shaped) ciirvod fvrvroiTds and 

 with itit respective sides connected below; and with distioct pplvio elements ; gills not 

 purao-.-.bap.-d, thiir ; xierual openings single on each 8i.l«: nostrils one on each side, 

 their openings often double; body variously formed, nsually scaly. . . . PisCKS. 



Beginning with the lowest, or least complicated of these groups we come now to the 

 consideration of 



CLASS I. MARSIPOBRANCHII. THE MYZONTS. 



Skeleton cartilaginous; the skull. inperfectly developed, not separate 

 from the vertebral column ; no ribs; no true jaws; no limbs; no shoulder 

 girdle nor pelvic elements; gills in the form of fixed sacs, without 

 branchiiil arches, six or seven in number on each side; a single nasal 

 aperture ; mouth subinferior, nearly circular, adapted for sucking ; heart 



