ee RR te et BE Coe a yet,» Rples CE RIS Ulgthna nee egret Ee Fs Fads Sheri, ORAL NEG UC TAY pp SO i a a RE REL ae TENNER Cee Te ae are Meme eS FY eine twee ee te 
a Trae 
pene Wee 
et ee 
SS) fe RE Ee Se orn Reema! 
on the Principle of Cephalization. 21 
As far back as 1855 he presented this thought in his lectures 
at Yale College. 
In the year 1862 Mr. Alpheus Hyatt had independently 
worked out a similar result, and has ase in MSS. notes, the 
necessary data demonstrating the sa 
Mr. Hyatt also proposes the name ay nna as more fully and 
truthfully expressing the type, than the unmeaning word Mol- 
lusca. ‘This name not only expresses the Plan, but is ae cae 
to the titles Vertebrata, Articulata, and Radiat ta, atid is 
way a cso appellation, 
Objecting as all must to the introduction of a new name, still 
one so appropriate as that proposed by Mr. Hyatt, in lieu of one | 
that has no relation to the Branch, except its traditional use, is 
certainly worthy of consideration, as it so clearly indicates what 
can believed to be the fundamental ‘idea i in the Branch, that of the 
essential structure of the animal, if rightly understood, must be 
our guide. The gradual morphological changes of the contents 
of the sac, and all other relations, are based on the principle of 
Cephalization. In the plate presented (Series J) I have given a 
typical figure of the six prominent groups of the Saccata; 
namely, Polyzoa, Brachiopoda, Tuni nicata, Lamellibranchiata, 
teropoda, and Cephalopoda. 
For obvious reasons, only the intestine, head, and pedal 
d in their normal position, anterior pole downward, the 
dorsal —— is turned to-the left. Commencing with the Poly- 
zoa, (Series I, P) we have the sac closed, while the mouth and 
anus terminate close i aeen at the posterior pole of the sac; 
the mouth occupying the me posterior position, and by a 
dorsal bend of the Gta upon itself, terminating dorsally, 
The nerve mass is found between the oral and anal openings, 
In this class the mouth and anus have the power of protrusion 
from the sac. In the three re orders, Cyclostomata, Ctenos- 
tomata, and Cheilostomata, t oon, when completely 
evaginated, presents no fold or eiecion of the sac, while in the 
higher group Phylactolamata, there is a partial me ee 
inversion of the sac under like conditions. © 
: hd wi and 
een us, and to him I am indebted not eal ae 
the of ; 
