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branches. But the occurrence of branch-scars and of diaphragms shows that the internodes are 

 really of the typical length ; and that branches have either failed to develop or have been lost. 

 When the stem has reached a certain age, a joint is formed in the region of the diaphragm, 

 and a similar joint occurs at the base of the branch. 



The basal view (fig. 4) of the zooecia is very characteristic. The zooecia of the two 

 series are usually alternate, with interdigitating inner walls; but are sometimes opposite, the two 

 zooecia being then separated by a wall nearly at right angles to the proximal and distal walls. 

 At about the middle of the basal surface occurs a single communication-pore, by which the 

 funicular tissue of the zooecium is continuous with that of the stem. On the outer side of the 

 pore, the basal surface gives origin to a circular group of retractor muscles of the polypide. 

 In the retracted condition, in which the specimens are preserved, the muscle-fibres appear very 

 thick and short; being contracted to such an extent that the lophophore lies close to the basal 

 wall. In parts near the growing tips many of the young polypide-buds are so placed that their 

 lophophore is visible from its distal side (fig. 5); and the young tentacles are clearly seen to 

 be 8 in number. In this stage of development the polypide-bud lies close to the basal and 

 outer side of the zooecium, which has already acquired nearly its full length. The lophophore 

 lies in the same position as that described above for the fully developed, adult polypide, in 

 its state of complete retraction; and its plane is parallel to the surface of the parent-stem and 

 almost in contact with that surface. The caecum of the young stomach lies close to the basal 

 wall, projecting towards the line which separates the two series of zooecia. At a slightly latei- 

 stage the tentacles are seen to be elongating in the direction of the principal axis of the 

 zooecium; the young polypide still lying entirely in the basal part of the zooecium. A mass of 

 cells, the commencement of the vestibule, is differentiated at the distal end of the tentacle- 

 sheath ; and at first lies well within the proximal half of the zooecium, in a position far removed 

 from the future orifice, with which it soon becomes connected by a fine thread. 



The zooecia in which the polypides are fully retracted are completely connate, as has 

 been described above. When the kamptoderm is everted a free cylindrical portion is formed, 

 as in the right hand zooecium of fig. 2. At the distal end of this is seen a comparatively 

 small collar. When degeneration of the polypide takes place, as in the next six zooecia of the 

 same figure, the everted kamptoderm, which has lost its vestibule and collar, forms a low 

 mammilla, marked by numerous circular cuticular striae. The form of the orifice, in zooecia 

 with a healthy polypide, is seen in the left part of the same figure, and is quadrangular, the 

 vestibule being about one third the length of the zooecium. The details of the alimentary canal 

 are not readily made out; but a distinct gizzard is present. 



The zooecia, which are somewhat variable in length, are about 600 — 700 u. long. Their 

 basal wall, as shown in fig. 4, is from 200 to 300 u. in breadth, and from 80 to looy. in length. 



In the specimens from Stat. 164(126. A., 507. B.) I have found a condition identical with 

 that described by Busk l ) in the specimens which he referred to A. semispiralis Kirchenpauer. 

 An internode, distinguished as such by a diaphragm at each end, is shown in Busk's figs 3^, 36 



1) Busk, G., 1886, Challengei Report, Pt L, p. 36, PI. VIII, figs 3, 3 a, 3/'. 



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