282 Dr Erichson on the Classification of 
guished by the stronger cirri which it supports, although the 
cirri do not so much belong to it as to the mouth; and how: 
little distinction prevails between it and the following seg- 
ments, is best observed where several eyes are present, and not 
on the first segment alone, but also on several of the succeed- 
ing. Lastly, what is termed a head in the Cestoids is in fact 
an cesophagus, as occurs often in the Annelides; and we re- 
quire only to compare a nereid with an cesophagus, with a 
tape-worm, in order to be convinced of the identity of the part 
in question. This connection will be more easily attained if 
we take a Sipunculus,or Priapulus, where the cesophagus is at 
the same time crowned with a circle of hooks. It appears to me, 
however, not altogether impossible that the Tzeniz can expand 
and contract this part just as well as the Nereids and Sepun- 
culus, although it may be immoveable in the Bothriocephalus. 
As the Vermes are thus, generally speaking, headless, so 
likewise there is awanting in them a central organ of the ner- 
vous system, a brain, such as is possessed by the Linnzean in- 
sects in the ganglion placed over the cesophagus,* and which 
here really gives the head its actual meaning. In the An- 
nelides, the first ganglion (or the cesophagal ring) has not the 
same importance as in insects, but the principle of life appears 
to be more distributed over the whole chain of ganglia, whence 
it is apparent how animals of this division, when cut in pieces, 
continue to live and are developed as individuals, whenever 
only a part of the ganglionic chain is preserved in the portion. 
In insects, limbs, at most, are reproduced. The principle of 
life is least of all centralized in polypi and planariz, in which 
separate pieces, divided at will, preserve their inherent life, 
and become entire animals. Probably the’ earliest centraliza- 
tion of the principle of life appears in the single portions of 
molluscous animals; but upon this subject we are not in pos- 
session of sufficient observations. 
* Thus, when in insects, the brain with the head is separated from the 
trunk, the movement does not cease, although the voluntary motion dies; 
at least I have never been able to convince myself that, after the loss of the 
head, the movements, which do not immediately cease, indicate a will inhe- 
rent in the trunk. 
