Miscellanea Zoologica. 07-3 



chise 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 first 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 Pycnogonidse have in reality seven pairs of 

 legs.f " 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 IYI. Latreille, and by myself, in individuals in his collection. 



* Latreille conjectured that the Pycnogonidie mghit respire by means of the 

 tubular abdominal segment, as some larva? are known to do, but the conjecture 

 has no observation in its support. 



f Savigny, Mem. sup. cit. 50. 



NO. IV. B b 



