VOGTIA PENTACANTHA. 



353 



Large specimens of Diphyes attain, 

 length of several inches, the stem 



ft w 



organs of reproduction, 

 when fully extended, a 

 giving support to at least fifty 

 different polypites. The other 

 genera of the order exhibit a 

 great variety in the form and 

 arrangement of their various 

 parts ; thus, in Vogtia, each of 

 the swimming organs (k) is pro- 

 duced into five points, of which 

 the three upper are much longer 

 and stronger, than the two lower. 

 The individual polyps (77-), large 

 in size, but few in number, are 

 congregated immediately under 

 the swimming apparatus, and 

 are provided with long and for- 

 midable tentacula. 



In the Physophoridse the 

 basal end of the common polyp 

 stem is modified so as to form a 

 float or aeriform sac, which is, 

 however, extremely different in 

 shape, structure, and size in the 



various families. In the Velellse, the float, whose under sur- 

 face is studded, besides one larger central polypite, with nume- 

 rous small nutritive, reproductive, and tentacular bodies, forms 

 a horizontal disc traversed by a diagonal triangular crest, and 

 divided into numerous hollow chambers. Thus equipped, the 

 semi-transparent velella, beautifully tinged with ultramarine, 

 sails on the surface of the warmer seas, but the currents of the 

 Grulf Stream, and the westerly winds, frequently drift it to the 

 coast of Ireland, where it is often found on the beach, entangled 

 in masses of sea-weed. Of the vast numbers in which it some- 

 times occurs, Herr von Kittlitz relates an interesting instance in 

 his " Travels to Eussian America and Micronesia." " Having 

 passed 30° N. lat. in the Pacific, the sea was suddenly found 

 covered with myriads of Velellae, of a size somewhat greater 

 than the Atlantic species. Two days long the ship sailed 

 through these floating masses, when suddenly the scene changed, 



^ 



a. Diphyes 



appendiculata. 



>. Vogtia penta- 

 cantha. 

 (Natural size.) 



