Dr. W. A. Herdraan on Dlazona and Sjntethjs. 167 



specimens of the ascidiozooids, a few drawings and some 

 notes, and then laid it aside with the intention of returning 

 to it again. 



I have now, since reading Mr. Garstang's interesting 

 remarks, re-examined the specimens of Diazona in my collec- 

 tion, which are : — 



(1) A colony labelled D. violacea^ from the Zoological 



Station, Naples ; 



(2) Part of a colony from near Plymouth, kindly sent to 

 me by Mr. Garstang ; and 



(3) The Hebridean colony, dredged by the Duke of 



Argyll to the north of Mull ; 



with the result that I believe them all to be the same species, 

 D. violacea. 



To take up the supposed points of difFarence : in the first 

 place, I find that many of the ascidiozooids in these preserved 

 specimens have the branchial and atrial apertures so obscurely 

 lobed that from the outside lobes cannot really be said to be 

 present ; and this is as much the case in the Naples and 

 Plymouth specimens as in the Hebridean one. But when 

 the test is removed and the siphons of the mantle are 

 examined under the microscope it is found that in all three 

 specimens each aperture is most distinctly six-lobed. In the 

 condition of the apertures, then, my Hebridean colony is 

 exactly like the southern forms, and in colour also the speci- 

 mens (in spirit) are alike. 



Then in regard to the number of transverse vessels or rows of 

 stigmata in the branchial sac, I find in an ascidiozooid from 

 the Naples colony over sixty rows, in one from the Hebridean 

 specimen I have counted sixty-seven rows, and may have 

 missed a few, and in the Plymouth specimen there are about 

 eighty rows. It is difficult to get the exact number, as the 

 rows are crowded in places ; but the above numbers are under 

 rather than over the mark, and they show clearly that the three 

 colonies are practically alike in the extent of the branchial sac. 



The next point is the number of stigmata in each mesh ; 

 and here I find very great variations in different parts of the 

 branchial sac * in all three colonies. In the specimen from 

 Plymouth 1 find most distinctly in some parts of the sac only 

 one stigma in each mesh. There is also a single stigma 

 behind each internal longitudinal bar, so that there are nearly 



* Lahille {he. cit. p. 257) figures, from Mediterranean specimens) 

 meshes containing one, two, and three stigmata each. 



