THEIR ALLIES. 77 
tacea do not have a distinct head, but rather a “head- 
thorax” (cephalo-thorax) . 
When we rise a third and last step into the world of 
Insect forms, we see a completion and final development 
of the articulate plan which has been but obscurely hinted 
at in the two lowest classes, the Worms and Crustacea. 
Here we first meet with a true head, separate in its struc- 
ture and functions from the thorax, which, in its turn, is - 
clearly distinguishable from the third region of the body, 
the abdomen, or hind-body. These three regions, as 
seen in the wasp, are each provided with 
<@ three distinct sets of organs, each having 
distinct functions, though all are governed 
by, and minister to the brain force, now in 
. a great measure gathered up from the pos- 
/ Fabr. ea W coe ` terior rings of the body, and in a more 
concentrated form (the brain), lodged in the head. 
Here, then, is a centralization of parts headwards ; they 
are brought as if towards a focus, and that focus the head, 
which is the meaning of the term “cephalization,” proposed 
by Professor Dana.* Ring distinctions have given away to 
regional distinctions. The former characterize the Worm, 
the _latter, the Insect. In other words, the division of. 
a transf mavens Damnoen | rs ae 
srt the otit tushaiio series. 
„Z, By the anterior of the locomotive organs participating to some extent in cepha- 
pi ET increased abbreviation, concentration, actness, and perfi 
structure, in the and organs of Of the aitarior portion of th of the body. perfection of 
reviation, condensation 
posterior, or or gastcic soe bee caudal portion of the’ perfection of structure in Hie 
phineesndon? aaa of the nervous system. This rise reach- 
