i ae ff 
* 
18 W. Gibbs on the Constitution of Organic Compounds. 
Nothing more than a passing allusion seems needed to the 
system of classifying the Mammalia on the modifications of the — 
placenta, originally proposed by Sir Everard Home,* and since 
reproduced and moditied by a few other naturalists. The group, 
e.g. associated by the character of the discoid placenta, is as_ 
little natural as that which would be composed on the basis of © 
the diphyodont dentition, or the unguiculate feet. The associa: 
tion of the Rodentia, and Insectivora, with the Quadrumana, as 
in the latest modification of the placentary system,+ is not likely 
to command acceptance. The diffused placenta, as in the Mare, | 
orpoise, Peccari, Rhinoceros, »and Camel, would lead to aa 
equally heterogeneous assemblage. In two well-defined minor 
groups, @. 7. the true Carnivora and the true Ruminantia, there — 
exist characteristic modifications of the placenta, viz. the zonular — 
and cotyledonal respectively; but thongh the zonular type is 
common to the Carnivora, it is not peculiar to them; it is that of 
the placenta in the Hyrax and the Elephant, amongst the Ungu- 
t. So likewise the on Botha type characterizes the pi 
of the Sloth among the 
sie % continued.) 
a 
oat TI1.—On the Rational Constitution of certain Organic BT 
unds ; by Wotcorr Gis, M.D., Professor of Chemistry 
Physics in the Free Academy i in New York, 
In the following memoir I shall endeavor to sainblish the ra 
tional constitution of several po diate pirat bodies by bee 
ring ther to the type of one or equivalents of water, 10 
which hydrogen is wholly or parily replaced by compo 
radicals. pane premises are as fol! 3 
ie electro-negative or aka hydrocarbons, formyl i 
CH, wet yl CsHs, and their homolo, ues, Day replace hyd 
equivalent for equivalent, but by su ak replacement diminish th 
electro-positive or zincous character of the primitive. 
facts are well exhibited in the acetyl-ammonia of Natanson, 
formula of which is 
C+H3 
N : 
2. The radicals formoxyl, Cs “HO: 2, acetoxy], CsHs0 
their homologues and analogues, similarly replace fo iM 
re ee more yrbibin y or chlorous derivatives. — 
tamin has the fi 
C+H2O2 
sti : 
H 
* Lectures on Comparative Ana vol. iii, 4 
+ Gervais, Zoologie et at Paléontologis' Peksasa te ios 1853, p- 194. 
