SOME ASCIDIANS FROM THE ISLE OF WIGHT. 147 



Both of Miiller's specimens were brilliantly pigmented, the whole of 

 the body within the test being of a bright crimson colour, except over 

 the area occupied by the viscera on the left side, which was whitish, 

 the intestine being of a livid green colour (" colorem luridum 

 exhibens "). 



But in Traustedt's specimens from Naples the red pigment was 

 found to be a very variable and unreliable characteristic ; sometimes 

 the stomach only was so coloured, sometimes this pigment was spread 

 over the entire area of the branchial sac (as in Miiller's specimens), 

 whilst sometimes individuals were taken which were quite destitute of 

 red colouration. 



Koule, at Marseille, has observed that the test is almost always rose 

 or red in colour, and he gives some beautiful figures in illustration 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 neighbourhood of Naples 

 and Marseilles. He describes the colour as " greenish or yellowish 

 white, seldom brownish, the oral syphon usually edged with red 

 (rothgesaumt) ; " further on he adds that the blood corpuscles 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 mentidoid forms at any rate ; and 

 Roule has quite rightly, in my opinion, merged Hancock's A. rubro- 

 tincta into the species A. mentula. Ascidia rubicunda of Hancock 

 agrees perfectly with the typical mentula of Miiller in its brilliant 

 colouration, and I shall show below how unimportant is the only other 

 character which distinguishes it from the general form of that species. 

 Ascidia robusta 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 distinct 

 correlation between the position and extent of the area of attachment 

 and the zone of the sea bed from which individuals have been taken. 



