628 PROFESSOR E. RAY LANKESTER. 



placed each in a completely closed chamber formed by the 

 growth of septa across the tube. When a bud reaches a cer- 

 tain stage in development it breaks through the wall of its 

 chamber and grows outwards in a direction forming a sharp 

 angle to the axis. At the same time the young bud which thus 

 bursts its prison wall forms a ring around the orifice of rupture, 

 and upon this a second, third, fourth, and so on, building up 

 its polyp-tube as it advances in growth (see PI. XXXIX, 

 fig. 1, e e). Thus each polyp-tube is connected with a distinct 

 chamber of the axis. It occasionally happens that the young 

 bud enclosed in an axial chamber of the tubarium does not 

 break its way out, but atrophies. Thus are produced the 

 ^'^ sterile chambers" noticed both by AUman and Sars. In the 

 specimens studied by me such chambers occurred (PI. XLI, 

 figs. 2, 6), but were very rare. It is probable that they are 

 produced more abundantly at one period of the growth of the 

 colony than at another. 



Both the axial portions of the tubarium and the polypide- 

 tubes may exhibit very sudden turns and twists. One of the 

 most remarkable cases of coiling of the tube which I have seen 

 is drawn in Pi. XXXIX, fig. 2. 



The living colony, which makes for itself the tubular habi- 

 tation just described, should perhaps have been dealt with 

 before the latter. There are advantages in both methods of 

 treatment, for it is easier to understand one when the other 

 has been already examined, whether we commence with 

 tubarium or zoarium. 



The Polypides. 



It will be convenient to note first of all various points 

 in the structure of the individual polypide, and then to 

 revert to the subject of bud-production and the method of 

 connection of the aggregate of polypides known as a colony 

 or zoarium. 



General Form. — A surface view, with natural colours, of a 

 polypide of Rhabdopleura Normani is given in Plate 



