PEOF. W. A. HERDMAN ON BRITISH TUNICATA. 443 



tliat there are really intermediate conditions between all of these 

 named forms. 



I have lately picked out three specimens of the typical 

 A. mentula, dredged from deep water (30-40 laths.) in Loch Fyne, 

 and three of the form which I regard as Hancock's A. ruhicunda, 

 collected from stones just below low-water mark in East Loch 

 Tarbert, and have compared them carefully, with the result that 

 although one can tell the dredged from the shore specimens 

 by the lighter grey colour and the slightly more delicate mantle 

 and branchial sac, still there is no structural difference that I 

 can find in any part of the body, and not even a difference in 

 degree that can be expressed in words and relied upon. Con- 

 sequently I am confirmed in my opinion that these are merely 

 two forms of th.e same species. 



"While making tbis comparison, I have had a useful lesson in 

 regard to the variability in number of the tentacles, and have 

 had my contidence in the published records of their numbers a 

 little shaken by the following observation. Miss J. H. "Willmer 

 (whose kind assistance in my laboratory in examining many of 

 these Ascidians I gratefully acknowledge) and I were noting 

 the characters of the above-mentioned six specimens of A. men- 

 tula, and as they were all large (over five inches in length) and 

 the tentacles seemed clearly visible to the eye, we merely turned 

 these organs over one by one with a needle in counting them, 

 and noted the results in numbers varying from 18 to 24. The 

 appearance of one example, however, made us suspect that 

 more tentacles were really present, and on dissecting out the 

 region and getting it in a good light under the microscope we 

 found that what had been visible before were only the more 

 prominent ones, and that from 70 to 80 tentacles were really 

 present. It was the same with the other specimens, all had 

 over 60, some nearly 100 tentacles. In the published records 

 by Heller, Traustedt, Garstang, myself, and others the numbers 

 vary from IG to 100, which does seem an extraordinary range ; 

 and I am tempted to suspect that I and others in tbe past may 

 have been deceived by a few of the tentacles being very con- 

 spicuous when in reality many othei's may have been present 

 in addition. 



84* 



