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I have had great difficulty in deciding whether all the specimens indicated above belong 

 to a single species or not. Hut as I have been unable to find satisfactory distinguishing features, 

 it seems best to consider that only one species is represented; and that the differences observed 

 depend on the state of development. 



This conclusion is supported by the fact that the zooecia on the same slide, and almost 

 certainly belonging to the same species, vary within wide limits. The young zooecia are relatively 

 short; while the old ones may be extremely long 1 ). Some of the oldest zooecia, indicated as 

 such by the large amount of mud in their ectocyst, are, however, not longer than many of the 

 young individuals. The evidence obtained points to the conclusion that on the degeneration of 

 the polypide the zooecia may shorten considerably, partly by contraction and probably in part 

 by the loss of the distal end of the peristome. In some of these cases (fig. 10) regeneration 

 ot the zooecium has occurred, the younger part being sharply marked off from the older part, 

 not only by a distinct line but also by having an ectocyst with few foreign inclusions. It thus 

 appears that in some cases the zooecium, after reaching a considerable length, may become 

 shorter on losing its polypide, and may then grow longer once more when regeneration 

 takes place. In other cases there is no great shortening when the polypide degenerates. 

 But as this process involves the loss of the vestibule, a new vestibule must be regenerated; 

 and this is probably accompanied by an increase in length of the peristome. Embryos have 

 only been found in large zooecia; a fact which may indicate that several generations of 

 polypides have been present, the zooecium having increased in size with each such occur- 

 rence. The extent of the differences observed is brought out by the series of measurements 

 recorded below. 



The peristomes are for the most part cylindrical along their whole course. The orifice 

 is usually square; but this is less obvious than in the following species (iV. annectens). The 

 vestibule is rather short. The collar is presumably present, but I have not obtained certain 

 evidence of its existence. If present it must be very delicate, and thus strikingly different from 

 that of N. annectens. The tentacles are about 18 in number, and are either quite straight 

 during retraction or are bent at their distal ends (fig. 19). The oesophagus is short, and is 

 succeeded by a distinct proventriculus. The caecum of the stomach is long. Strong parieto-vaginal 

 muscles are inserted into the vestibule; and parietal muscles are present, their fibres being 

 generally arranged two in a group. 



Daughter-zooecia, commencing as stolon-like threads, are given off from the base of the 

 cylindrical part of the zooecium. Four are often present, arranged in the typical cruciform 

 manner. But a complication is introduced by the fact that the "stolons" may bifurcate. If the 

 division takes place at their point of origin, the zooecium may appear to give rise to a larger 

 number of "stolons", up to as many as eight. Each such tube is separated from the parent- 

 zooecium by a diaphragm, although the tube which represents the proximal end of the parent- 

 zooecium may show no diaphragm. The zooecium in such cases consists of a thread-like proximal 



1) A similar variability has been noticed by SMITT (1865, "Om Hafs-Bry. utveckl. och Fettkr.", Üfv. K. Vet.-Ak. Förh., Arg. 22, 

 p. 30; and 1S66, »Krit. förteckn." II, Arg. 23, p. 525, PI. XIII, fig. 39), in the species of the same genus described by him as Farrtlla 

 and Vesicularia fusca. 



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