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deo-eneration (fig. 9). The distal end of the zooecium is now rounded. In others the collar has 

 been lost, and has probably been thrown off 1 ), all traces of the vestibule having also disappeared. 

 Some of these old zooecia are considerably longer than the individual shown in hg. 3, and a 

 polypide-bud, or a young polypide, may be visible in their interior. It is natural to suppose 

 that this would lead, in course of time, to the reconstitution of a normal orifice ; and some of 

 the variability in the length of the peristome may be the result of the successive formation of 

 one or two polypides: each such formation being accompanied by au increase in length of 

 the zooecium. 



Fig. 4 shows the general structure of a zooecium. The strong collar is well seen in 

 its retracted position, and the vestibule is provided with very strong parieto-vaginal muscles, 

 running obliquely from the body-wall into the vestibule. The tentacles are moderately long; 

 and they appear to be not less than 16 in number. The examination of other specimens 

 shows that they are not less than 20, in some cases at least. The pharynx is short, and, in 

 its retracted condition, lies close to the proximal end of the zooecium. The oesophagus is of 

 oreat length and passes distally, to about the region of the middle of the bundie of tentacles. 

 Here it opens into a large proventriculus, which may represent the gizzard of some other 

 Ctenostomes. The proportions of this limb of the alimentary canal are different from those 

 shown by Calvet -), in a longitudinal section of N. dilatata. The stomach and its caecum are 

 large, and the rectum is slender. A series of strong parietal muscles is present, on each side, 

 in the proximal end of the zooecium. The examination of other specimens shows that the fibres 

 are arranged in groups. 



The arrangement of the alimentary canal shown in fig. 4 is, however, not constant; and 

 in fig. 7 it may be seen that the apex of the retracted caecum is directed distally. In some of 

 the very long zooecia above described the alimentary canal has a U-like form, in correlation with 

 the large amount of space available. The great elongation of the oesophagus is a characteristic 

 feature of the present species. 



The variability in the size and relative proportions of the parts of the zooecia will be 

 brought out by thé following measurements, in u. : 



Fig. 1 ; total length of the zooecium, including its narrow proximal part, measured along the 

 curve, 4000 ; greatest diameter, 240 ; diameter of the narrow proximal portion, 40 — 60. 



Fig. 3; total length, 2600 ; diameter of the distal half of the peristome, 150. 



Fig. 4; total length, 1670; greatest diameter, 350; diameter of the distal end, 120. 



(Not figured); total length of an old zooecium which has no narrow proximal part, and in 

 which the polypide has degenerated, 5920. 



Length of peristomes, measured from the angle formed with the terminal daughter-zooecium : — 

 Fig. 1, 180; Fig. 8, 220; Fig. 7, 570; Fig. 4, 1000 ; Fig. 5, 1050 ; Fig. 3, 2150. 



In several of its characters the present species shows a considerable resemblance to 



1) Braem (1914, "Knosp. v. Pahtdictlla", Avch. f. Hydrobiol. IX. pp. 539, 540) has described the throwing off of the tentacular 

 apparatus, or a part of it, on the degeneration of the polypide in Pahidkdla. 



2) Calvet, L., 1900, t.cit., PI. VII. tig. 12. 



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