Miscellanea Zoologica. 373 
chiae is admitted, but neither can it be shewn that they breathe 
through tracheae after the manner of spiders : it is probable that the 
aeration of the circulating fluid is effected by the mere contact of the 
water in which they all live with the external surface, a mode of 
respiration not unknown among some of the less perfect crustace- 
ans.* To determine whether or not they agree in the number of 
legs with Arachnides may seem an easy matter, and upon the de- 
termination the question of their location mainly depends. If we 
merely reckon the number of members used for locomotion, the 
agreement is exact ; there are four pairs in spiders, and four pairs in 
the sea-spiders ; but Savigny's researches appear to have proved that 
some parts have been overlooked which ought properly to enter into 
the calculation. By tracing, with the hand of a master, the muta- 
tions of the organ through the more remarkable families of crusta- 
ceans and apterous insects, he lirst shews that the so-called proboscis 
of the Pycnogonum is a head, without any analogy with the sucker 
of some acaridans ; and were the Pycnogonidse to be classified with 
the Arachnides they would be anomalous there ; the only cephalous 
family in the class. The proboscis being admitted to be of the na- 
ture of a head, the conclusion necessarily follows that the members, 
whose true character is concealed under the designations of mandi- 
bles, palpi, and oviferous organs, are merely modifications of the 
legs, which have undergone less change of form than the corre- 
sponding legs in many other families of the Crustacea ; so that, like 
the crustaceans, the Pycnogonida? have in reality seven pairs of 
legs.t " If we attentively examine," says Savigny, " the mandi- 
bles and palpi, we must conclude that the family of the Pycnogonum 
is that in which these organs differ least, either in position or in 
usage, from the ordinary feet. Their insertion is very far removed 
from the aperture of the pharynx, which is often placed beyond their 
reach ; the insertion is made not into the head, nor to the advanced 
segment which supports the head, but immediately to the thorax. 
The palpi are not attached to any sort of jaws. And what is to be 
thought of the total occasional suppression or obliteration of these 
organs ? In fact, if the Nymphons have both palpi and mandibles, 
the Phoxichiles have mandibles only, and the Pycnogonum has nei- 
ther mandibles nor palpi. These curious facts have been observed 
by M. Latreille, and by myself, in individuals in his collection. 
* Latreille conjectured that the Pycnogonidffi mghit respire by means of the 
tubular abdominal segment, as some larvae are known to do, but the conjecture 
has no observation in its support. 
f Savigny, Mem. sup. cit. 56. 
NO. IV. JJ b 
