374 Miscellanea Zoologica. 
Nevertheless, the three genera seek the same aliment, they are all 
equally carnivorous, an unanswerable proof that the parts to which 
the names of palpi and mandibles have been given in the Nymphons 
are not necessarily employed in manducation ; that the mouth has 
its proper existence independent of those parts ; that it is essential- 
ly composed of other organs, and this point is so decisive that we 
may doubt whether the Pycnogonidae, hitherto arranged with the 
Arachnides, would not be placed with greater propriety among the 
Crustacea."* 
Some naturalists cannot coincide in this suggestion, because of the 
great simplicity of the anatomy of the Pycnogonidae, which is very 
inferior to that of the Crustacea. The simplicity of their structure 
must be admitted ; the alimentary canal appears to be a straight 
intestine extended between the mouth and anus, with some lateral 
expansions or cceca ; and the circulating system is probably reduced 
to a single vessel which occupies the centre of the thoracic segments, 
and sends a branch to each member or limb, in which the blood has 
an irregular movement, but cannot be said properly to circulate. 
The rest of their anatomy is unascertained. But the argument 
hence deduced is one which will equally forbid their admission 
among the Arachnides, for the typical spiders are little less highly 
organized than the typical crustaceans ; and M. Edwards has shown 
that, by assuming anatomical characters as the basis of classification, 
the most unnatural combinations would be the result, so that even 
they who have advocated the superiority of these characters, have 
found an adherence to their principles quite impracticable in the 
classification of avertebrate animals. It is a better and safer me- 
thod to arrange these animals in as many groups as there are dis- 
tinctly recognizable series formed by the successive simplification or 
degradation of each distinct organism. In this way we are not ar- 
rested by differences of anatomical structure,Hvhen these are con- 
fined to mere differences of complexness ; and, in the instance of the 
Crustacea, we attach to the class all those species whose general or- 
ganism, however simple, has no deviations incompatible with that of 
the types of the class, but which simplicity is, if we may so speak, 
the result of an arrest to its developement, and recalls by its simila- 
rity, the transitory conditions through which the most perfect con- 
stituents of the class have passed during the continuance of their em- 
bryonic life. To proceed thus may seem to be acting contrary to the 
recognized principles of natural systems, and one is apt to be start- 
led at a proposal to gather together in one category animals which 
* Mem. sup. cit. 75-6. 
