VOGTIA PENTACANTHA. 353 
organs of reproduction. Large specimens of Diphyes attain, 
when fully extended, a length of several inches, the stem 
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 (v) is pro- 
duced into five points, of which 
the three upper are much longer 
and stronger than the two lower, 
The individual polyps (7), 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 Physophoride the 
basal end of the common polyp 
stem is modified so as to form a { 
float or aériform sac, which is, ,* Deut. age aoa 
however, extremely different in ee 
shape, structure, and size in the 
various families. In the Velelle, 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 
Gulf 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 Russian America and Micronesia.” ‘ Having 
passed 30° N. lat. in the Pacific, the sea was suddenly found 
covered with myriads of Velellz, of a size somewhat greater 
than the Atlantic species. Two days long the ship sailed 
through these floating masses, when suddenly the scene changed, 
Foor 
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