REPORT ON THE TUNICATA. 31 



about 3 mm. in diameter ; they are arranged with considerable regularity in rows, the 

 Ascidiozooids in adjacent rows alternating wdth one another (PI. II. fig. 11). The inner 

 surface of the test next to the common cloaca is perfectly smooth and glistening. The 

 atrial apertures of the Ascidiozooids are conspicuous rounded openings up to 1 mm. in 

 diameter (PI. II. fig. 12). The thickness of the colony, from the outer to the inner 

 surface of the test, is from 1 em. to 1"2 cm., and that is, of course, also the antero- 

 posterior length of the fully developed Ascidiozooids. 



The fragment preserved in picric acid has both the branchial and atrial apertures 

 larger and more conspicuous than in the spirit specimens, probably because the picric 

 acid has not contracted the tissues so much. The atrial apertures are especially large, 

 and are rounded openings with no lobes (PI. II. fig. 12). They vary from about I'S mm. 

 to 3 mm. in diameter, and are arranged with considerable regularity in alternating 

 rows. This picric acid specimen is not, however, in good condition for histological 

 examination. The small fragments preserved in alcohol arc much better in this respect. 



The branchial sac is very large. There are at least thirty internal longitudinal 

 bars on each side of the endostyle, and over fifty transverse vessels on each side. The 

 ciliated cells of the transverse vessels are large and distinct, and there are about twelve 

 cilia on each cell (PI. II. fig. 14). The meshes formed by the intersection of the 

 transverse vessels and internal longitudinal bars are elongated transversely, and are 

 about two to three times as long as they are wide. 



There are at least ten long narrow languets along the dorsal edge of the branchial 

 sac. In other respects this species agrees in structure with Pyrosoma giganteum. 



The dorsal tubercle has a circular aperture which leads, l)y means of a bent tube 

 running along the under surfiice of the ganglion, to a triangular subneural gland 

 (PI. II. fig. 13). 



The testis is composed of a large number of caeca, certainly over twenty (PI. II. 

 fig. 15) ; while in the other species there are only about a dozen cseca. 



Undetermined Specimens of Pyrosoma. 



The following specimens of Pyrosoma, either on account of their bad state of 

 preservation, or because of their being very young colonies, cannot be determined as 

 to their species with certainty. 



(1.) A very young Pyrosoma colony was obtained l)y means of the tow-net on 

 April 12, 1876, Station 351 ; North Atlantic ; lat. 9' 9' 0" N., long. 16° 41' 0" W. ; surf 

 temp. 81°'8. It is a small octagonal plate 2 mm. in diameter and slightly over 1 mm. 

 in thickness. At the angles the test is produced into short, pointed spines, and there 

 are four pale yellow Ascidiozooids embedded in the clear test (PI. II. figs. 1-4). 

 When examined under a 1-inch objective the colony presents the appearance shown in 



