6 VERTEBRATA. 
possession of a cellular cord, — the ‘ notochord,’ — which runs un- 
derneath the central nervous system, and which in the higher forms 
is surrounded by the permanent vertebral column and skull, and is 
largely obliterated by the development of these structures. So the 
term CHorDATA is frequently employed as synonymous with VER- 
TEBRATA in its wide sense.” (Rh. R. Wright.) 
Without further discussion of the VERTEBRATA or “ CHOR- 
DATA” as a whole, we may proceed to the account of the several 
subordinate groups or classes. The existing forms may first be 
divided into about six primary groups, which have been called 
“ provinces ” by Professor Huxley. ‘These are (1) the Urochor- 
data, including the class Tunicata ; (11) the Hemichordata or En- 
teropneusta ; (III) the Cephalochordata, corresponding to the class 
Leptocardii; (1V) the Ichthyopsida, including the classes of Cyclo- 
stomi, Pisces, and Batrachia; (V) the Sauropsida, including the 
Reptilia and Aves; and finally (VI) the Mammalia, correspond- 
ing to the single class of the same name. 
The relations of these provinces and classes are shown in the 
following analysis taken, in part, from Dr. Gill’s “ Arrangement 
of the Families of Fishes.” Only the more obvious characters 
are here mentioned. Others may be found in the more elaborate 
works on Comparative Anatomy. 
Analysis of the Classes of Chordata. 
a. Anterior end of the central nervous axis not dilated into a brain, and not 
surrounded by a protective capsule or skull. 
6. Notochord confined to the tail and usually present only in the tadpole- 
like larval stage of the animal (UROCHORDATA): adult animal not 
fish-like nor hikinanrs its body invested with a tough envelope or 
** fMIG. Fak ‘ ‘ be Nea ha Moe Ug 2 li ON INC SA a 
bb. Notochord not Canad to the tail, but extending forward to the anterior 
end of the body; sides of body with numerous gill slits which are 
persistent through life. 
d. Notochord developed in anterior end of body only (HEmMIcHoR- 
DATA): adult animal worm-like, without trace of fins; a long 
proboscis before the mouth. . . . . . ENTEROPNEUSTA, B. 
dd. Notochord perfect, continued forward to a point before the mouth 
(CEPHALOCHORDATA) : body elongate, lanceolate, somewhat fish- 
like in form, not worm-like nor enveloped in a ‘‘tunic’’; middle 
line of body with Sy a fins; no proboscis; the mouth slit- 
like, fringed with) irr) 2% : .'. » Leprocarpn, C. 
aa. Anterior end of the nervous axis dilated into a ‘‘ brain,’’ which is con- 
tained within a protective capsule, the ‘skull notochord not 
continued forwards beyond the pituitary body; heart developed and 
divided into at least two parts, an auricle and a ventricle. (CRaA- 
NIOTA.) 
e. Respiration during part or the whole of life performed by means of 
gills; blood cold. (ICHTHYOPSIDA.) 
