SOME xVSCIDIANS VllOM THE ISLE OP WIGHT. 135 



rose or red iu colour^ and lie gives some beautiful figures iu illus- 

 tration of this condition^ but he also admits a considerable degree 

 of colour-variation in the species,, which he attributes to local 

 influences. 



Heller's specimens from the Adriatic seem to have been much 

 more subdued in colour than those from the neighboui'hood of 

 Naples and Marseille. He describes the colour as " greenish or 

 yellowish-white, seldom brownish, the oral siphon usually edged 

 with red {rothgesaumt) ; " further on he adds that the blood-cor- 

 puscles are brownish. My specimens, therefore, approach Heller's 

 very closely in this respect. 



Now a perusal of Hancock's paper on Several New Species of 

 Simple Ascidians (1870, 1. c.) shows that he attached a considerable 

 importance to distinctions of colour in his definitions of species, an 

 importance which can no longer be admitted for mentuloid forms at 

 any rate ; and Roule has quite rightly, in my opinion, merged 

 Hancock's A. rubro-tincta into the species A. mentula. Ascidia 

 ruhicunda of Hancock agrees perfectly with the typical mentula of 

 Miiller in its brilliant colouration, and I shall show below how un- 

 important is the only other character which distinguishes it from 

 the general form of that species. Ascidia rohusta of Hancock is 

 distinguished from the specimens which I have described from the 

 Isle of Wight by hardly any other point than the prolongation of the 

 oral and cloacal siphons. 



It may be observed that in all the mentuloid forms there is a dis- 

 tinct correlation between the position and extent of the area of 

 attachment and the zone of the sea-bed from which individuals 

 have been taken. The Ascidia mentula of authors is an inhabitant 

 of the deeper waters, and is found attached usually to stones and 

 shells by its base and a very little of the left side. Adhering in 

 this way, it is obvious that it has an erect position upon the sea- 

 bottom. Now the three species named above were distinguished by 

 Hancock from Ascidia mentula partly on account of the mode of 

 their attachment; A. ruhrotincta adhered ''by the middle portion 

 of the side," A. ruhicunda "by the whole side with imperfect mar- 

 ginal expansions," A. rohusta ''by the whole side, but [was] some- 

 times much distorted, and with adherent root-like prolongations." 



These three " species " were all taken from between tide-marks, 

 the first at Guernsey, the second at Tobermory (Isle of Mull), 

 Portaferry (Strangford Lough), and Bertraghbuy Bay (Connemara), 

 the third at Herm. 



The Isle of Wight specimens also were attached by the whole or 

 the greater part of the left side, and they also were taken from a 

 rock at low water. 



