CONTRIBUTION TO KNOWLEDGE OF RHABDOPLEURA. 643 



PLATE XXX VIII. 



Fig. 1. — A single polypide of Rhabdopleura Normani, Allman, as seeu 

 wlien issuing from the mouth of its tube. Highly magnified. The tube, 

 •which would reach up to about the level of the letter B, is not represented. 

 A. Mouth. B. Anus. C. Polypide stalk (contractile stalk, soft stalk, or 

 gymnocaulus). D. The buccal-disc or shield (prseoral lobe). E. The intes- 

 tine, showing through the rounded posterior projection of the "abdomen." 

 F. The richly-pigmented thorax. G. A gill-filament or ciliated tentacle of 

 the left tentaculiferous (lophophor) arm. /. The transparent abdomen, the 

 yellow colour due to the gastric epithelium showing through. 



Fig. 2. — A lateral view of a similar polypide. The left tentaculiferous arm 

 is incompletely drawn for the sake of clearness. Letters as in Fig. 1, with 

 the addition of K. Sars' ciliated sense (?) organ. Oa. Axis of the right 

 tentaculiferous arm. 



Fig. 3. — A similar polypide seen from the anal aspect, the tentaculiferous 

 arms incompletely drawn. Letters as in Figs. 1 and i, with the addition of 

 Dp. Pigment spot of the buccal-disc (probably a rudimentary eye). 



Figs. 4, 5, 6, and 7 are intended to show different positions and forms 

 assumed by the buccal-disc. In Fig. 1 its flat surface is thrown upwards, in 

 Fig. 2 the disc is bent on itself so as to make the flat surface concave. In 

 Fig. 4 the disc is elongated, and the pigmented extremity stretched forward ; 

 in Fig. 5 it has contracted to a nearly pentagonal form ; Fig. 6 gives a view 

 from the oral aspect of the position shown in profile in Fig. 2 ; Fig. 7 gives a 

 profile view corresponding to Fig. 5, 



Fig. 7. — The letters are as follows : — d. The broad or flat surface of the 

 buccal-disc. 0. Gill -filament (in outline). H. Raised margin of the tenta- 

 culiferous arm, where it joins the circum-oral region of the thorax. Ga. Axis 

 of the tentaculiferous arm. 



Fig. 8. — Extremity of a gill-filament or tentacle, to show the disposition of 

 the pigment in the epithelial cells. 



PLATE XXXIX. 



Fig. 1. — A portion of a colony of Rhabdopleura Normani, Allman. 

 Highly magnified. Comprising a gemmiferous or growing branch, a (to the 

 left), and six complete polypides with their tubarium. a. Extremity of the 

 growing branch, showing the deeply-notched form of the growing margin of 

 the tubarium, due to the bifid form of the foot of the immature polypide q, 

 by which the segments of this part of the tubarium are secreted, b. Soft 

 stalk or gymnocaulus of the terminal polypide of the growing branch, c. 

 Youngest or latest bud produced by the gymnocaulus, cl. Penultimate bud, 

 that part of the stalk which produced it having now ceased to be " gymno- 



