REPORT ON THE TUNICATA. 101 



(PL IX. fig. 13a). The cells of the lower surface and sides are diamond-shaped or short 

 fusiform, and have distinct point-like nuclei (PL IX. fig. 13b and c). Those of the 

 band along the upper edge are cubical or low columnar, in most places the latter, and 

 have nuclei placed near the lower end of the cell, and only seen in a profile view (PL IX. 

 fig. 13e). A surface view of the dark hand shows the ends of these columnar cells as a 

 series of closely placed minute round areas (PL IX. fig. 13d). Underneath the epithe- 

 lium in the tentacles are placed here and there large spicules similar to those of the 

 branchial sac (PL IX. fig. 13a, sp.). In the interior of the tentacles may also be seen in 

 many places small collections of the large round yellowish-brown blood-corpuscles (PL 

 IX. fig. 13a, b.c). 



The Prcebranchial Zone or the area lying between the branchial siphon and the 

 branchial sac, and bounded superiorly by the circlet of tentacles and inferiorly by the 

 peripharyngeal band, is in this species of moderate breadth (PL VIII. fig. 7). It is 

 about one-third of the length of the larger tentacles, and the smaller tentacles mostlv 

 extend just across it to the peripharyngeal band. It is perfectly smooth, and is covered 

 by squamous epithelium in direct continuity with that covering the lower surface of the. 

 tentacles. 



7'//c Peritubercular Ann, or the dorsal offshoot from the prcebranchial zone, in 

 which the dorsal tubercle is placed, is triangular in shape (PL VIII. fig. 7, and PL IX. 

 fig. 15), nearly symmetrical, and relatively large, being nearly twice as long as the breadth 

 of the prcebranchial zone. 



The Dorsal Tubercle, better known perhaps as the "olfactory" tubercle, is small, and 

 is situated down in the posterior angle of the peritubercular area (PL VIII. fig. 7, and 

 PL IX. fig. I 5, </./.). It is, however, distinctly visible, and has the form of a hemi- 

 spherical projection, on the surface of which is a deeply cut groove forming a crescent 

 with both horns curled inwards. The horns are anterior and posterior, and the concavity 

 is turned towards the left side. 



The Peripharyngeal Band, bounding the pnebranchial zone posteriorly, is well 

 marked, and has the usual form of a pair of closely placed ridges separated by a narrow 

 groove. At the dorsal edge of the sac, where the two halves of the peripharyngeal band 

 turn posteriorly to bound the peritubercular area, the right half is rather higher or more 

 .■interior than the left (PL VIII. fig. 7, J>.j>.). At the apex of the peritubercular area the 

 two halves unite at the anterior extremity of the dorsal lamina. 



The Nerve Ganglion is of small size, and has an elongated fusiform shape (PL IX. 

 fig. 15, n.g.). It lies immediately posterior to the dorsal tubercle, its anterior extremity 

 overlapping that organ dorsally. 



The Heart is situated on the right side of the body. It lies on the inner fare of the 

 mantle towards the ventral edge, about midway between the branchial and atrial aper- 

 tures, and is placed longitudinally, running parallel with the endostyle, from which it is 



