836 MR JAMES RITCHIE ON 



by polypiferous offshoots, similar to the stolon proper, which arise from the proximal 

 dilatation of the polyp-stalk close to where it and the stolon join. Frequently two off- 

 shoots arise from the same dilatation — on one occasion four were observed. The 

 cuticle of the stolon is generally much wrinkled transversely ; it is extremely delicate, 

 and in preparations mounted in Canada balsam has frequently collapsed. The stolon is 

 divided into regular polyp-bearing segments separated by barren ones of irregular 

 length. Muscle-fibres are absent from it except towards the extremities of offshoots, 

 in the neighbourhood of the growing point, where a thick layer of ectodermal cells 

 exists. That the chitinous nodes, which limit a polypiferous segment of the stolon, 

 develop subsequently to the budding of the polyp is evident ; for in the younger polyp- 

 bearing offshoots no node occurs in the neighbourhood of the base of the stalk, although 

 in older examples such exists. An abnormal separation between stalk and stolon is 

 shown in PI. I. fig. 2, where a horizontal septum at the base of the stalk takes the 

 place of the usual vertical pair placed in the stolon, one on each side of the stalk. 



Stalk. 



The stalk consists of a variable number of internodes separated by well-developed 

 chitinous nodes, through a circular perforation in which a coenosarc connection runs. 

 Three and four are the most common numbers of internodes, but five and six 

 occasionally occur, while seven and eight are rare, and are found on old stalks almost 

 always destitute of calyces. Thus, in 75 individuals examined, the segments of 

 whose stalks varied in number from 2 to 8 (single-jointed individuals being ignored), 

 the distribution was as follows: — 18 individuals possessed 2 segments, 23 had 3, 22 

 had 4, 7 had 5, 3 had 6, 1 had 7, and 1 had 8. All the internodes, except the primary 

 and the terminal, are of the same structure. The primary internode is a cylinder 

 which arises from one of the smaller segments of the stolon, such as has already been 

 described. The basal portion of this first stem internode or "phalanx," to use Ehlers' 

 term, is broad, but the distal narrows rapidly, forming a cone-like summit, truncated by 

 the first stem node. Like the nodes, the walls of this cone-like portion are chitinous and 

 of a distinctly yellow colour. The median internodes consist of a narrow chitinous tube 

 which arises from the summit of the previous internode, which varies very greatly in 

 length, and which gradually widens into a swelling similar, except in volume, to that of 

 a primary internode, terminating like it in a chitinous cone truncated by a nodal septum. 



The terminal node differs from this general type, for the median dilatation, instead 

 of ending in a chitinous cone, is produced into a gradually narrowing tube, upon the 

 summit of which the calyx is perched asymmetrically. The chief features of this 

 terminal internode are its great length, the absence of a rigid chitinous envelope from 

 all but the basal portion, the continuation of the muscle-fibres to the distal end of 

 the internode, and the presence at this end of a thick bed of ectodermal cells lining the 

 inner surface of the cuticle. Those structures, with the exception of the last, are 

 clearly adaptations to facilitate movement, and observation of a living individual shows 



