6 J. D, Dana on Cephalization. 
pond to the four in Spiders plus a preceding pair of mouth- 
organs. The head and locomotive part of the thorax in the 
Land-Articulates appear to correspond unitedly, as stated by 
Latreille, to the cephalic portion of the Crab, that is, to nine an- 
terior segments out of the fourteen cephalo- thoracic. In other 
words, this part of the body of an Insect is an extreme concentra- 
tion of the anterior portion of a Crustacean—an example of ex- 
treme cephalization ; while a Crustacean is a diluted Insect, being 
much Sesto and more numerous in segments and mem mbers 
obster (or any ordinary Macrural Decapod Crustacean) 
has an n eligi body, and an abdomen well developed and far- 
nished below with a full series of mémbers. In the male Crab, 
also a Decapod, the body is very short, and the abdomen is with- 
out its members, besides being so small that it folds into a 
groove in the under shell of the bo ody; this diminution of size 
and increased compactness are a inpregeree of the "Grabs t ce- 
is dais 6 f the riobest instincts under the Articulate type. 
From these examples it is evident that where there is a com- 
pacting of the body connected with rise in grade, it is not merely 
a general compacting of the different parts alike, or a genel 
concentration and perfecting of the system, but a true cephaliza- 
tion of the system,—the compacting and seer showing itself 
primarily in a greater concentration, predominance, and domina- 
tion of the cephalic extremi 
Among Articulates having feet, an Insect and a Limulus stand 
at the opposite poles of cephalization. The mouth-organs and 
= in both correspond to those of the head (or the mouth- 
appears to be no reason to doubt that, in all types, not Laie oes: 
gat pair of members BASS excluded) correspon nds to a separate segment 
of the pine at Audouin & Edwards are sustained in their views on this point by 
the fact, that in a Squilla, three anterior cephalic segments (those of the eyes and 
two none of antenne) and four Besterion thoracic are actually cates and in an 
aie 
being presen 
obsolet nsect, * the Saute seit, fos PON arias to oe | 
ea three to the thorax); in the latter, two-thirds (or fourteen); the 
dominal, | iscera are ; a Crustacean (exce 
F | 
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