i6 



I have had lampreys full of ova when not more than four 

 and one- half inches long ; these were of a bluish grey color 

 and died within a few days after removal from the brook, 

 seemingly requiring cold running water. 



From the fact of their having spawn when of such a small 

 size, I would suggest the propriety of maintaining the sub- 

 species or variety Petromyzon marinus nigricans of Lesueur, 

 although the latter has lately been regarded as merely the 

 young of the sea lamprey. 



Class Pisces. 



Fishes. 

 A fish is an aquatic vertebrate, with a developed skull and a 

 lower jaw; the limbs are weak ; four, two or rudimentary, 

 forming the pectoral and ventral fins. The dorsal, caudal and 

 anal fins are part of the mechanism of locomotion , of the nature 

 of keels and rudders. A fish swims mostly by means of his 

 tail, the limbs serving only for the subsidiary movements, in 

 some cases also for walking, i. e. , crawling along the bottom 

 or climbing up stones, logs, etc. The shoulder girdle is almost 

 always attached to the skull by clavicle bones, and is some- 

 times rudimentary. The pelvic arch is frequently only 

 embedded in the muscles or it may be rudimentary, or altogether 

 absent. The skin is either naked, or covered with scales or 

 plates of a horny or bony texture. The respiratory organs, 

 called gills, are comb-like plates attached to the gill arches; 

 the swim bladder, when present, sometimes gives indications 

 of being a sort of lung. 



Sub-class Teleostomi. 



Perfect or True Mouths. 

 The skeleton is developed ; the gills (usually four pairs) are 

 attached to the arches by the bases only and are covered by 

 the opercles ; the gill opening behind and below the opercles is 

 single on each side. The heart has one auricle, one ventricle, 

 and an arterial bulb. The hemispheres of the brain are not united. 



Series Ganoidei. 



The skeleton is cartilaginous or ossified. The tail is hetero- 

 cercal or diphycercal ; some fins have fulcra. The exo-skele- 



