n6 VELELLA SPIRANS. PAET m. 



margin. A similar system exists both in the upper 

 and under-surface of the disk. All these systems are 

 connected with one another, and with organs pending 

 from the inferior side of the disk, which are hid when 

 the Velella is in its natural horizontal position. These 

 organs consist of a large central sterile polypite, which 

 supplies the whole system with elaborated juices ; it is 

 surrounded by smaller polypites, which are both nutri- 

 tive and reproductive ; and the whole is encircled with a 

 ring of prehensile and armed tentacles fastened to the 

 rim of the disk, immediately adjoining to the under- 

 side of the limb. The pneumatic filaments already men- 

 tioned are mixed with these different organs. 



In the Velellidse caught by M. Vogt, he invariably 

 found the stomachs of the large as well as of the small 

 polypites, full of the carapaces of minute Crustacea, 

 shells, the bones of small fishes, and larvae, so as even to 

 be swelled out with them. The indigestible parts are 

 thrown out at the mouth, and the elaborated juices are 

 transferred to the various systems of canals to be dis- 

 tributed through all the members of the animal. The 

 mouths of the small polypites take various forms; some- 

 times they are wide and trumpet-shaped, with everted 

 lips, sometimes they are contracted. These small poly- 

 pites consist of a double sac, fastened to the disk by a 

 hollow stem with many rounded elevations on their sur- 

 face full of thread-cells. The tentacles of the Velellidee 

 are strong, thick, club-shaped tubes, completely closed 

 at their extremities, which abound in thread-cells ; their 

 cavity is filled with a transparent liquid, supposed to 

 play an important part in their elongation. 



Medusiform zooids are formed on the slender stems of 

 the small polypites. It is presumed that they lay fer- 

 tilized eggs which yield Yelellidse, so that this animal 

 has probably alternate states of existence ; but nothing 

 is known of its earliest stages of development. The 



