106 DPv W. A. HERD MAN ON 



4th intermuscular space posteriorly. Keferstein and Ehlers represent it as 

 extending rather further anteriorly, but terminating at the 4th muscle band 

 posteriorly ; while in Grobben's figures it commences as in mine, but terminates 

 in the 3rd intermuscular space. At its anterior extremity the endostyle is 

 joined by the ventral ends of the two peripharyngeal bands (see PI. XVIII. 

 figs. 7 and 11), while posteriorly it is continued into a membrane with a free 

 projecting edge which runs backwards over the heart, and then round the left 

 hand side of the oesophageal aperture (PI. XIX. fig. 10, mb). The histology of 

 the endostyle has been minutely described by Grobben (loc. cit.). 



The prebranchial zone, the region anterior to the peripharyngeal band, is 

 covered by squamous epithelium. In osmic acid preparations the protoplasm 

 in these cells is found to have become contracted and aggregated around the 

 distinct nuclei, so as to present the appearance, shown in Plate XIX. fig. 6, 

 of stellate cells united by their processes to form a network. 



On- the surface of the peripharyngeal band this epithelium has become 

 modified into long fusiform cells (PI. XIX. fig. 5) all placed with their long axes 

 directed along the band. When not so highly magnified, or not stained 

 properly, they give rise to the appearance shown in Plate XVIII. fig. 13. The 

 dorsal ends of the two peripharyngeal bands meet, but at this point they are 

 twisted round so as to form a double spiral towards the right, the left hand 

 band performing one and a half turns, and the right a single turn only. This 

 arrangement is shown in figs. 8, 11, and 12 on Plate XVIIL, and at once 

 suggests the form of the dorsal tubercle found in a similar position in the 

 Ascidiacea. That organ is represented, however, in Doliolum, not by the curved 

 dorsal part of the peripharyngeal band which has been described, but by the 

 anterior end of the deeply funnel-shaped depression indicated by n.a in figs. 8 

 and 12.* 



The part of the prebranchial zone which is enclosed by the dorsal spirals of 

 the peripharyngeal band has its epithelium modified into large polygonal cells, 

 the outlines and nuclei of which are strongly marked. In the preparation from 

 which fig. 7 on Plate XIX. was drawn, the protoplasm in most of the 

 cells was aggregated around the nucleus in a stellate form. 



The nerve ganglion is placed in the mantle, and indicates the median dorsal 

 line. It is small, but very distinct from its opacity. It is usually rudely cubical 

 or nearly spherical in shape, and gives off four large nerve trunks, two at its 

 anterior and two at its posterior angles, besides smaller nerves between. It 

 usually lies a short distance behind the 3rd muscle band, as shown in figs. 8 



* Possibly the cavity {n.a in the figures) represents merely the opening of the duct from the 

 neural gland into the dorsal tubercle of the Ascidiacea, while the spirals {d.t, in PI. XVIIL fig. 11) 

 indicate the sense-organ, which I believe the dorsal tubercle to have formerly been (see Proc. Roy. 

 Soc. Edin,, p. 144, 1882-83. 



