96 W. BLAXLAND BENHAM. 



Fig. 19. — The rostellum in the same stage as in Fig. 18 — at the com- 

 mencement of protrusion. The distal wall of the acanthophore is seen 

 to be invaginated as a thin membrane (j), to which the radial muscles 

 (e) are inserted. The longitudinal and circular muscles of the rostellar 

 wall are shown (L. C), the latter extending up to the upper insertion 

 limit of the hooks. The granular contents {t) are represented with 

 the greatest care. They show granulation and fibrillation and nuclei, 

 and are seen to be confined to the reservoir. The details of the recep- 

 taculum are also faithfully represented ; the contents of the mem- 

 branous sacs (*) appear to coagulate or shrink, leaving a space, so that 

 the cells appear to form an epithelium. 

 Fig. 20. — The rostellum only is shown in a fully protruded condition. 

 The section is not quite median so far as the acanthophore is con- 

 cerned, hence the distance between the booklets is not as great as 

 it would be if the booklets were at the ends of a diameter. The 

 reservoir is strongly contracted, so that the contents {t.) have been 

 entirely forced against the " radial muscle " (e.), and thus distend the 

 acanthophore. The radial muscles are practically vertical (cf. Fig. 19), 

 and the invaginated membrane {j.) into which they are inserted is 

 pushed forwards so as to become convex. The contraction of these 

 muscles in this condition, when their area of insertion ( j.) is rendered 

 tense, raises the points of the booklets so as to effect attachment to 

 the wall of the gut. 

 Fig. 21. — Transverse section through the rostellar apparatus about the 

 middle of its length. R. Rostellum. r. Receptaculum rostelli. L. I. 

 Longitudinal musculature. C. c. Circular muscular of each. The rostellum 

 is seen to be filled with finely granular material, in which are nuclei, n. 

 Nuclei. The coarsely granular contents of the receptaculum are contained 

 in four sacs (5.), the walls of which meet to form four septa {w). 



Fig. 22. — A. transverse section of the receptaculum below the rostellum. 

 Letters as before. 



