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i. Mimosella bigeminata Waters. (PI. VII, rïgs i — -7). 



Mimosella bigeminata Waters, 1914, "Mar. Fauna Brit. E. Afr.", "Bry. Cycl. . . .", Proc. Zool. 

 Soc, p. 851, PI. III, figs 1 — 3 (Zanzibar Channel, 10 fathoms). 



38. M. Stat. -j-j. Borneo Bank. 3°27'S., 117° 36 E., 59 Metres; fine grey coral-sand. 



396.O. Stat. 162. Between Loslos and Broken Islands, W. coast of Salawatti, 18 Metres; 



coarse and fine sand with clay and shells. 

 123, A. Stat. 164. i°42'.5 S., I30°47'.5E., 32 Metres; sand, small stones and shells. 

 359. C. Stat. 240. Banda Anchorage, 9 — 36 Metres; black sand, coral, Lithothamnion-bank. 

 374. D. Locality and depth not recorded. 



Zoarium Stirparia-\\ke, consisting of much elongated, attenuated, unbranched sterns rising 

 from a basal series of rootlets or stolons. Erect sterns jointed, commencing with a few barren 

 segments, follovved by one or tvvo with a single pair of zooecia ; the remaining stem-segments 

 bearing two pairs of zooecia at their distal end. Zooecia long, subcylindrical, provided with a 

 proximal cone of muscles by which they are no doubt moved on the bracket-like support from 

 which they originate. Vestibule short, with a very delicate collar. Tentacles 8. Alimentary canal 

 not folded during retraction. A slight dilatation of the alimentary canal, at the junction of the 

 oesophagus with the stomach, may be the morphological equivalent of a gizzard; but a structure 

 actually of this nature can hardly be said to be present. 



There can be little doubt of the corrrectness of the reference of this species to Mimosella, 

 a genus which has the peculiarity of having its zooecia moveable on their stalk-like proximal 

 ends. Hixcks has given a good description of these movements, from observations made on 

 living specimens of M. gracilis l ) ; and he compared the movements of the zooecia with those 

 of the leaflets of Mi?//osa, the Sensitive Plant. He was unable to find any special muscles *), 

 which could be regarded as the agents of these movements. In the 'Siboga' specimens it is 

 easy to recognise these muscles in a group of cone-like form, situated at the extreme proximal 

 end of the zooecium. The muscles in question originate in the bracket-like projection which 

 supports the zooecium, and diverge to be inserted into the inner side of the body-wall of the 

 zooecium (fig. 3). In suitably orientated specimens it can be seen that the cone consists of a 

 pair of groups of fibres. Hincks' observation that the movements of the zooecia continue after 

 the loss of the polypide is accounted for by the fact that the muscular cone does not disappear 

 when histolysis of the polypide takes place. The movements may perhaps be affected by a 

 special arrangement of muscles, described below, in the stem-segments. 



The general characters of the species may be illustrated by a description of the specimen 

 shown in hg. 5. The erect stem originates from an internode of the creeping stolon from which 

 rootlets diverge in various directions over the substratum. The stem is divided into segments 

 by diaphragms; and at each such point it is jointed by a slight annular thinning of the cuticle, 

 which is elsewhere sufficiently developed to give the stem-segments a rigid character. The first 

 stem-seo-ment is lono- (2160 u.) and bears no zooecia. It is foliowed bv three other barren 



1) Hin-cks, T., 1851, "Notes Brit. Zooph.'', Arm. Mag. Nat. Hist. (2) VIII, p. 359; and 1880, "Hist. Brit. Mar. Pol." pp. 556, 558. 



2) They have, however, been figured by Joliet (i888, "Études Pyresoma Rech. Bry. Roscoff et Menton'\ Paris, p. 112, 



PI. V, fig. 5 wc) and by Waters (1914, t.cit., PI. III, fig. 1). 



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