366 POLYZOA INFUNDIBULATA. 



PLATE LXXL 



Sarcochitum polyoum, Hassall in Ann. and Mag. N. Hist. vii. 484. 



Hah. Parasitical on Fucus serratus. 



" This species is also usually found investing Fucus serratus, the 

 frond of which it sometimes covers to the extent of several inches. 

 The crust is thin and fleshy, and covered with numerous large emi- 

 nences of irregular form and unequal size, which exhibit a puckered 

 appearance in the centre, and from which the polypi issue; these 

 have twenty tentacula. The polypidom, when found on one side of 

 the weed, is generally also present on the reverse side ; and this is 

 somewhat curious, as the crust almost constantly terminates on each 

 side of the weed at some distance from its edge, ' so that it cannot 

 reach the one side from the other by a continuity of growth. 



" The ova in this species are exceedingly numerous, and vary in 

 colour from white to yellow; they present much the same form and 

 appearance as those of the preceding genus. If a quantity of the 

 sea-weed, with the zoophyte upon it, be placed in salt-water for a few 

 hours, great numbers of the ova will become liberated, and may 

 plainly be seen with the unassisted eye moving about^ in almost 

 ceaseless action; now gliding rapidly along the surface of the water, 

 now wheeling round upon their axes ; at one time elevating them- 

 selves in the fluid, again as rapidly sinking in it these elevations 

 and subsidences seeming to depend upon the form of the ovum, which 

 is seen to change with these movements. The facility and rapidity 

 with which these little bodies seem to perform their evolutions is very 

 striking. They may often be seen to run along the water in a 

 straight line for several inches, at a pace which would far outstrip 

 the fleetest Newmarket racer the relative sizes of the two creatures 

 being taken into consideration; and it is not a little curious to 

 observe, that, no matter how many ova be moving about in the same 

 space, still they never come in contact, appearing to avoid each other 

 as carefully as though they were possessed of eyes. 



" The thought then occurred to me, that the minute, frail, and 

 delicate ova of these species must have made their way unscathed 

 and uninjured through from twenty to thirty miles of the troubled 

 and stormy ocean, and have fixed themselves to our rocks the vi- 

 bratile cilia on their surfaces being mainly instrumental in effecting 

 their transportation. 



" The polypidoms of this and the preceding species are often so 

 mixed up in their distribution upon the same piece of sea-weed, that 



