ON TRACHEAN ARACHNIDA. 
525 
duct from the crabs to phalangium, we might believe, that 
nature, in subtracting from the Crustacea their anterior 
organs, and replacing their tail by an abdomen, thus con- 
verted them into arachnida. But, admitting this hypothesis, 
it would still be necessary to pass from the nymphons to the 
arane’ides, or to the arachnida called pedipalpi, and it would 
not be very easy to explain the mode adopted by nature in 
operating this new transformation. 
As the interior organization of the pycnogonides is unknown, 
it is not possible to determine the place which these singular 
animals should occupy in the natural series of created beings. 
Nevertheless, as they appear to have, in spite of some ano- 
malies, great relations with chelifer and phalangium , affinities 
which had already been remarked by celebrated naturalists; 
— as the body of many trachean arachnida also presents an 
anterior articulation, supporting analogous mandibles and 
palpi ; — as the tubular sucker of the pycnogonides may be 
nothing but an union of jaws and under lip prolonged and 
cemented ; — as the absence of composite eyes, and the exist- 
ence of a tubercle supporting the simple eyes confirm these 
relations ; — as the feet of the pycnogonides are composed of 
nine articulations, a character for which we should seek in 
vain in the Crustacea, but which we shall find in several of these 
arachnida ; — as in giving to the pycnogonides feet as long, and 
a linear form adapted to their habits, Nature has been obliged 
to extend their thorax to the prejudice of their abdomen, which 
is here represented by a small articulation in the form of a 
tail ; — M. Latreille was originally determined to place these 
animals between the pseudo-scorpions, and the phalangia. 
In his work called “ General Considerations on the Natural 
Order of Crustacea, Arachnida, and Insects,” the pycnogonides 
alone form an order, which unites the parasite insects, such 
as the pediculi and ricini, to the acerated, or arachnida. 
The nymphons are distinguished from the pycnogona by 
