ON Ee EPR eT ee ee leh acea 
J. D. Dana on Cephalization. _ 5 
Crustaceans consists rather in their degradational characters than 
in any peculiarities of the — In the tribe of Ostracoids 
(Cypris, etc.) alone, one genus has two pairs of mouth-organs, 
the rest being legs, another ites and another four, the Tetra- 
decapod nu amber 
TIL Mollusks.—It has been remarked that the subkingdom of 
Mollusks cannot, from its nature, exemplify the first method of 
cephalization. The methods exemplified are the third, fourth, 
ninth and tenth. In the transition from the order of Cephalo- 
pods—the first—to that of Uephalates (Gasteropods),—the second—. 
there is a loss of the feet or arms, and a diminished perfection 
of the senses, and activity is reduced to sluggishness. Descend- 
ing to the third order, or Acephals, the antennz fail, the eyes be- 
come imperfect or obsolete, locomotion becomes very imperfect. 
and in some fails altogether. Among —— a still inferior 
order, all the organs of the senses fail, and t is the radiate 
structure of vegetation as well as its sessile shefceen 
The difference in cephalization between an oyster and a clam 
is very strongly marked, the oyster, when placed in its normal 
position, having its body nearly all posterior to the beak, being 
—_ a large gastric mass, and the clam having one-third of 
ly anterior to the eak, and really exhibiting something 
masely:3 in mien compared with the oyster. 
Other illustrations of the subject might be given; but they 
are not necessary to explain the general principle in view 
The number of pairs of feet in the subkingdoms of Vertebinide 
and Articulates, under those types which afford eee of the 
method of cephalization, is as follows 
I. VERTEBRATES. 
1, in Man; 2, in all other Vertebrates. 
‘TL. ArricuLatEs. 
1. Under Insecteans : 3, in es A, in Pes rs. 
2. Under Crustaceans : 6, i ; 7, in Tetradecapods. 
The number oe rs of ‘feet in the different groups are then 
1,2, 2, 4, 5, 7. one case of typical transfer occurs in each of 
the three pee: ustrating the subject, Mammals, Insec 
and Crustaceans; and these cases occur uniformly between the 
two highest orders ‘of the class. 
Man’s title to the place assigned him in our former paper 
8% therefore to be unquestionable. ol 
The types of tiger = and Articulates do not admit of 
Roeclogical compari a4 
The types of Thnsetenias and Crustaceans are modifications of a 
pone on types et the two are so widely different, that it is far 
Crustaceans corres- 
the Jive pairs in the highest 
