1256 General Notes. [ December, 
The Mammalia have been traced to the Theromorphous rep- 
tiles by the Monotremata. The birds, some of them at least, ap- 
pear to have been derived from the Dinosaurian reptiles. The 
reptiles in their primary representative order, the Theromorpha, 
have been probably derived from the Rhachitomous Batrachia. 
The Batrachia have originated from the sub-class of fishes, the 
Dipnoi though not from any known form. I have shown that 
the true fishes or Hyopomata have descended from an order of 
sharks, the Ichthyotomi, which possess characters of the Dipnoi 
also. The origin of the sharks remains entirely obscure, as does 
also that of the Marsipobranchi. Dohrn? believes the latter class 
to have acquired its present characters by a process of degenera- 
tion. The origin of the Vertebrata is as yet entirely unknown, 
Kowalevsky deriving them from the Ascidia, and Semper from 
the Annelida. à 
It is now possible to determine the nature of the evolution of 
the greater number of the vertebrata, by resolving the difficult 
problem of distinguishing primitive from degenerate types. »Y 
degeneration I understand loss of parts and organs which subserve 
what would be usually called animal vitality, as distinguished 
from vegetative life. Preéminent among these must be regard d 
varied powers of movement, which give the greatest opportunity 
for the exhibition of intelligence. Loss of parts without comple- 
mentary development of other parts is the usual form of degeneration. 
Among the true fishes there are several examples of degener- 
ation. Among Physostomi the marine eels (order Colocephali) 
exhibit this in their skulls and fins, the final degradation being 
reached by the deep-sea form, the Eurypharyngide. In ee 
clysti, the group with abdominal ventral fins descended rae < 
the Hemibranchi to the very degraded type of the Lophonrm a 
The group with pectoral ventral fins, especially the Percomani 
present us with a degraded type of the Plectognathi. e re 
scent commenced in the suborder Epilasmia (Chaetodontice, 
Teuthyidz, etc.). It is 
The Batrachia are almost entirely a line of degradation. ~ de) 
now quite safe to say that the Trachystomatous order (Sireni 
is a degraded, and not a primitive type. rae : 
The lines of Reptilia Chii terminated in the existing a z 
a line of degradation. In comparison with the Theromo 
Crocodilia are degraded, and the Lacertilia ar 
This latter order displays within itself the most rema 
ber of degraded forms, as I can agree with Dr. Boule! sig 
p . d their alli 
calling them. Among snakes, the Typhlopidæ an , 
are a degraded type, but the order displays a pa 
on the whole. Two extinct orders of Reptilia show 
1 Proceedin ri i . Sdciety, 1884, p. 585- : i Nos 
2 gp som anag aren ha pa Si unctionwechsels 
Anton Dohrn, Leipsic, 1875, p. 32. 
