284 STUDIES ON TUNICATA, 



with the dredge; they are always more flaccid than those from the 

 tidal zone, and the body within the test is disproportionately 

 small. The branchial aperture is eight-lobed, the atrial six-lobed,^ 

 both very prominent in living specimens but completely retractile. 

 The siphonal lobes are all ornamented towards their base with a 

 small bright red spot. The colour of living specimens is light sea- 

 green, preserved specimens are yellowish or grey. 



The test is moderately thick, but transparent. The external 

 layer is firm and tough, the innermost layers so gelatinous, 

 as to be almost viscid. Test cells are of the typical stellate 

 variety; their processes are small and few, so that they appear 

 round or oval at first sight. 



The mantle Q>\iteY\0Y\y is strong, muscular, and perfectly trans- 

 lucent. The opacity of the anterior end is not pronounced in 

 living specimens; it is due to the abundance of muscular tissue 

 which, in preserved specimens, being contracted, intensifies the 

 opacity by puckering the mantle. The longitudinal muscle 

 bands are external to the transverse; each arises by two thin cords 

 from the adjacent sides of contiguous siphonal lobes (PI. xxvii. 

 fig.13) on the branchial siphon. At the base of the atrial siphon 

 these bands divide and, coursing across the left and right towards 

 the ventral side and posteriorwards, broaden out and become 

 evanescent before the posterior end is reached. The dorsal side 

 and posterior end of the mantle bear transverse muscle-fibres 

 only. 



The branchial sac is delicate; its vessels of attachment, though 

 fine, are stronger than the sac itself. There are no folds present. 

 The transverse vessels are alternatel}' large and small; the inteinal 

 longitudinal vessels are about equal to the larger transverse in 

 size. The meshes are broader than long, and with great constancy 

 contain each seven stigmata. The internal longitudinal vessels 

 bear opposite each transverse a large spatulate papilla, and along; 

 the larger transverse bars there extends a very delicate membrane. 

 There are occasionally fine transverse bars between those already 

 described; no papillae are present at their intersection with the 



