98 
On VARIATIONS in the DORSAL TUBERCLE of 
Ascidia virginia. . 
By Amy E. Waruam, B.Sc. 
With Plate VII. 
[Read December 9th, 1892.] 
In a paper read before the Royal Physical Society in 
1881, Professor Herdman, F'.R.S., described and figured 
several varieties of the dorsal tubercle in Ascidia virginia, 
to show the range of its variability. At his suggestion I 
have lately taken the opportunity of examining nearly 
AO individuals of this species with the following results :— 
There appear to be two simple forms of dorsal tubercle, 
and several variations from each of these. One of these 
simple forms is ovate, rounded posteriorly, with the two 
‘“‘horns’”’ straight, and inclined towards each other, but 
not curved (Plate VII., Nos. 1—5.) The other is almost 
circular, the two horns curving towards each other, and 
each horn forming a semicircle. (Nos. 283—26). No. 21 
shows an intermediate form. 
1. The first variety of the ovate form occurs when one 
horn curves slightly inwards the other remaining 
straight (Nos. 6 and 7). 
2. Next, both horns curve inwards. (No. 8). 
3. One horn may reach more anteriorly than the other. 
(Nos. 9 and 10). 
4, The longer one shows a tendency to turn outwards. 
(QO, LN), 
5. The same horn shows a slight, distinct, outward turn 
(No. 12) which becomes more marked in Nos. 13 
and 14. 
