SEA-NETTLKS. 99 



other extremity of the main bladder there is an orifice, through which the 

 animal has the power of contracting the bladders to force out the air within; 

 and thus by repressing the buoyant power, at once" sink beneath the waves. 

 That it has likewise the means, by some internal economy of generating fresh 

 air, to renew the supply when it desires to take a .sail, is equally certain; 

 and although the apparatus by which this is effected is not understood, it is 

 not difficult to conceive the existence of chemical agents by which it might 

 easily be effected. 



As these animals are mostly seen floating on a calm sea in the bright 

 sunshine, it is not impossible that the supply of air being just sufficient to 

 cause it to rise to the surface; the air contained within the bladder may 

 become rarified, and hence more buoyant, needing therefore less real waste 

 than under any other circumstances. All that we see is the delicate body 

 and the bright purple velamina, but depending from this are the same organs, 

 which are found in various forms in all the medusae, in the shape of tenta- 

 cula and root-like substances, constituting in fact the animal itself; and 

 busily employed probably in feeding, while it appears merely to be basking 

 in the bright rays. 



Another very beautiful specimen of this order is the Ghelyosoraa, which is 

 composed of a disc, more or less transparent, regularly traversed by tubular 

 substances, which branch out as they approach the circumference, and take 

 something of the shape of the Shepherd's purse corallines, and around the 

 circumference is a connected string of small bladders of equal size, which 

 when distended, appear like a pearly diadem lying on the bosom of the 

 green ocean. From these, numerous filaments descend of a considerable 

 length, and by these, subsistence for the medusa is obtained. These are the 

 types of an order only, and as such are usually adverted to, and it would be 

 manifestly impossible in a paper on the different tribes of Marine Animals to 

 enter moi-e into detail. 



Two genera of AcaJephoe now only remain to be described, but none of 

 those already adverted to are more worthy the attention of the naturalist. 

 The first of these, the Girrhigrada, bear a close apparent resemblance to -the 

 Pahnonigrada, being supported in the water by a circular concave disc, but 

 in this disc we recognise a semicartilagenous structure, which approaches to 

 the formation of a shell; and is composed of lamina, obliquely placed against 

 each other in rows, extending in straight lines from the centre to the cir- 

 cumference like radii, and these are full of hollow cells. From this shield, 

 as it were, cirrous, or tufted tentacula depend, and some species have an 

 elevated ridge on the upper circumference of the disc, from which a thin 

 membrane is produced, which, catching the air, wafts the little creature on 

 its voyage of pleasure. 



Next and last, we have the Diphyida, which have long puzzled the 

 learned, as it is wholly uncertain whether they arc composed of two separate 

 individuals adhering together, or of one so delicately joined as to raise the 



