310 Transactions. — Zoology. 



Fig. 4, from a specimen treated with osmic acid, also shows 

 faintly the squamose epithelial cells in outline (m.). 



As before mentioned, the branchial siphon is plain-edged, 

 and widens gradually, ending in the muscular ring from which 

 the numerous tentacles spring (fig. 4, b.t.). The tentacles are 

 all of equal length, their points meeting across the buccal 

 cavity. 



The normal four rows of branchial stigmata are present, 

 most clearly distinguishable in the young zooid (fig. 10) on ac- 

 count of the greater opacity of the mantle in the adult stages. 

 Still, four rows were distinctly traceable in the mature zooid, 

 the cilia fringing them being faintly seen. A row of large 

 "fringing cells" (fig. 9,/.c.) outline the stigmata very clearly, 

 and also indicate the limit of the longitudinal vessels (l.v., 

 fig. 9). The transverse vessels (t.v.) are much broader than 

 the longitudinal. The fringing cells have large oval nuclei, 

 which stain deeply, especially with picro-carmine. Other 

 deeply-stained nuclei are also found (fig. 9, nc.) over the 

 branchial vessels : these no doubt indicate the cellular struc- 

 ture of the branchial basket. 



The endostyle (figs. 2, 4, and 10, en.) is large and distinct. 

 In transverse section it appears square, and with obj. C the 

 columnar epithelial cells can be discerned (fig. 4, en.). Its 

 course is very undulating (fig. 2, en:), ceasing indistinctly near 

 the oesophagus. When viewed from below, as in fig. 2, a 

 clearer space appears in the centre : this is due to the fact 

 that the epithelial cells here are not piled upon each other, 

 being viewed endways only. 



The dorsal lamina is represented by a series of long 

 languets, situated transversely on the transverse vessels of the 

 branchial sac (fig. 9, d.l.). They are broad at the base, and 

 flattened, the edges being fringed by large cells distinctly out- 

 lined. (See note on peripharyngeal band at end of descrip- 

 tion.) 



A small nerve ganglion (n.) and larger neural gland (n.g.) 

 are seen in all transverse sections through the upper region of 

 the branchial sac (figs. 4, n. and n.g., and 10, n.). 



The alimentary system is remarkably complex, and ap- 

 pears to offer peculiarities hitherto unrecognised. The oeso- 

 phagus, after narrowing greatly at the oesophageal constric- 

 tion (te.c, fig. 2), widens again, and passes soon into the 

 cardiac division of the stomach, which is large and thick- walled 

 (fig. 7, St.). In longitudinal section the stomach has a bobbin- 

 shaped lumen (PI. XXIX., fig. 8), and is seen to exhibit traces 

 of columnar epithelial cells of great length composing its walls. 

 The stomach is then continued as a pyloric sac about equal to 

 the oesophagus in size where it leaves the stomach, but 

 dilating distally into a bulb, in many instances, before passing 



