14 SURFACE FAUNA OF THE GULF STEEAM. 



(PI. XI, Fig. 5), and are not arranged in sets of three, as they are represented 

 by Kiiniker as charaoteristic of the Mediterranean .species. The tubules com- 

 mence about the outer edge of the white plate, and are most numerous towards 

 its central part (PI. XI, Fig. 2), where they come to the inner surfoce, 

 and literally cover it with a matting of winding silvery threads (PI. XI, 

 Figs. 1, 4). Towards the centre of the float they become less numerous 

 again (PI. XT, Fig. 3), ending with six or seven tubules, which take their 

 origin near the eight primary chambers, and extend over that part of the 

 float. 



Porpita is not as easily upset as Velella ; and the number of specimens 

 thrown ashore by the winds is very small, as compared to the numbers of 

 Velellie stranded on the beaches after every storm. Porpita is capable of 

 considerable control over its movements. Owing to the great size and power 

 of its numerous long marginal tentacles, it can readily force itself back again 

 into a normal attitude, if upset by the wind or waves. It can, by bringing 

 its tentacles together over the disk (PL X, Fig. 1), and throwing up the free 

 edge of the mantle slowly in a given direction, then expanding the tentacles 

 of one side far over on the opposite direction beyond the central part of tlie 

 disk, it can thus readily change the centre of gravity, and tilt the disk Ijack 

 again into a normal attitude, should it from any cause have been set afloat 

 with the tentacles uppermost. The larger outer marginal polypites are ar- 

 ranged in three or four irregularly concentric rows, with two to three inner 

 rows of smaller knobbed tentacles, in all stages of development (PI. X, 

 Figs. 2, 3, 10, 11). Inside of these are arranged, in from five to six similar 

 rows, round the base of the large central polypite, the small, stout, flesh- 

 colored feeding and reproductive pol3'pites (PI. X, Figs. 4, 5). These have a 

 slightly rectangular head (PI. VIII, Figs. 1-4), capable of considerable 

 expansion, with four clusters of lasso-cells at the thick rounded angles 

 of the terminal opening. At the base of these polj'pites are found Medusae 

 buds in all stages of development (PI. VIII, Figs. 1-4 ; PI. X, Fig. 4). At 

 the time when in full reproductive power these clusters of Medusae complete!}^ 

 fill the whole space between the small polypites, giving to the ring which they 

 occupy on the lower surface of the float a dark yellowish tint from the color 

 of the yellow cells found along the rudimentary proboscis of the MedusK 

 buds, as well as along the chymiferous tubes (PI. VIIT, Figs. 1, 2, 4-11). 



The large marginal tentacles (PI. X, Fig. 3) are of a bluish tint, the ten- 

 tacular knobs of a darker color. The internal cavity of the tentacles has a 



