two new Genera of Irish Zoophytes, 485 



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 ra- 

 pidly along the surface of the water, now wheeling round upon 

 their axes ; at one time elevating themselves 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 faciUty 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 vibratile 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 it requires a practised eye to distinguish them. I 

 have been induced to consider this species as distinct from 

 the genus Alcyonidium, to which it bears a near relation — for 

 the. following reasons: 1st. The number of the tentacula, a 

 character which I have found to be constant, it being twenty 

 in this and but sixteen in Alcyonidium', 2nd. This species 

 never rises from the surface of attachment in the form of an 

 independent polypidom ; it is invariably encrusting, whereas 

 all the species of the genus Alcyonidium do form elevated 

 polypidoms ; and 3rd. There is a difference in the form of the 

 body or organ to which I have referred in the description of 



