a 
SYSTEMATIC RELATIONS OF FISHES. 579 
middle finger a little longer than the thumb. If there should be 
an arrest of development at this stage, the track would be birti-like. 
Next, the fourth finger makes its appearance, and, on the hind 
feet, the fifth comes still later. What is especially interesting is 
that when the legs or feet have been amputated, which frequently 
occurs, the operation being performed by those miniature fresh 
water sharks, the larvæ of dragon flies and water beetles, the 
development of the toes is precisely in the same order, first the 
three toes, then the fourth, and on the hind feet the fifth. The 
gills are now beautifully plumed and when closed reach to the 
centre of the entire animal ; hind legs starting. June 20, fifty-six 
days, hind feet developed. 
As the lungs increase the gills wither and are gradually ab- 
sorbed, so that by the middle of August the gills have all disap- 
peared. The time consumed in the wonderful process is a little 
over one hundred days. 
OBSERVATIONS ON THE SysTeMATIC RELATIONS OF THE FisHEs.—By 
Pror. Epwarp D. 
I. PRELIMINARY. 
Tue system of fishes as at present adopted in this country, is 
the result of the labors of many naturalists, but chiefly of Cuvier, 
Agassiz, Muller and Gill. Without going into the history of the 
subject at present, it will be proper to point out the principal 
modifications of Cuvier’s system, introduced by his three succes- 
sors. The orders of Cuvier were the Chondropterygii, Malacop- 
terygii, Acanthopterygii, Plectognathi and Lophobranchii. 
Professor Agassiz, under the name of Placoids, adopted the first 
division; the second he called the Cycloids, the third Ctenoids, 
and then created a fourth order under the name of Ganoids, which 
should embrace a portion of Cuvier’s Chondropterygii (the stur- 
geons), a portion of the Malacopterygii Abdominales (the bony 
gars, etc.), and the two last orders of Cuvier. Professor Müller 
following, with a still more complete anatomical investigation, 
especially into the soft parts, discerned three swb-classes in Cu- 
vier’s Chondrostomi, which he named the Leptocardii (lancelet), 
Dermopterit (lamprey, etc.), and the Selachii (sharks, etc.). In 
the then recently discovered Lepidosiren he saw a fourth sub-class, 
Dipnoi. 
AMER. NATURALIST, VOL. V. 37 
