SOME ASCIDFANS FROM THE ISLE OF WIGHT. 123 



It is represented of the natural size on PI. VI, figs. 5a and 5 b, and 

 deprived of the test, by fig. 6. The body is not compressed from 

 side to side (right to left morphologically) like an ordinary Ascidian 

 and like normal individuals of the same species, but dorso-ventrally ; 

 and thus it comes about that, although attached in the usual manner 

 by its left side, its right side does not present a flattened surface, but 

 is elevated so as to form a thickened longitudinal ridge of considerable 

 height. 



The dimensions are as follows : 



Length (antero-posterior) . . .2 inches. 



Breadth (dorsal-ventral across the plane of 



attachment) . . . . • I ^^ 



Thickness (morphological right to left) . | ,, 



The breadth becomes considerably reduced towards the summit of 

 the ridge which represents the right side of the body. 



The test is very thick and presents all the characters of normal 

 individuals of Ascidia mollis, except that it is much corrugated on 

 that face of the body which contains the cloacal aperture (see 

 fig. 5 a). The oral aperture is sub-terminal and on the same side as 

 the cloacal aperture, which is slightly nearer the anterior than the 

 posterior end of the body. The body is attached by almost the 

 whole of the left side, which is deeply furrowed and irregularly 

 pitted. The test is overgrown by extensive colonies of the Polyzoon 

 Cylindroecium dilatatum. 



Upon removal of the test, the extent of the dorso-ventral com- 

 pression is at once noticed. The ganglion and cloacal siphon, in- 

 stead of occupying their usual position upon the apparent left of 

 the body, are in the median line of the upper side ; and the whole 

 of the viscera appear to have suffered a similar rotation through 

 90 degrees. Strictly speaking, however, the viscera present exactly 

 the same morphological relations to the rest of the body as in the 

 normal individuals described above. 



The generative organs are well developed, and the oviduct and 

 vas deferens are remarkably dilated. The former contains 

 numerous ripe ova, of small size ; and the latter is filled with a 

 mass of spermatozoa. 



The only difference of any importance in the pharynx is the pre- 

 sence of a pharyngo-cloacal slit,^ \ inch in length, in the usual 

 position opposite the cloacal aperture. 



The prsebranchial zone is closely studded with minute papillee. 



The growth of the aperture of the dorsal tubercle has progressed 

 still further ; both horns are now curved inwards. 



Epipharyngeal groove and dorsal lamina as in younger speciuiens 



* See p. 132, 



