BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 345 



into the floor of the anterior chamber. He now refers to the posterior chamber, 

 which, he says, occupies the centre of the muscle of the organ, a modified but 

 scarcely satisfactory description. The external granular glands show certain 

 peculiarities when contrasted with other species, viz., complete separation, large 

 number and minute size of the divisions or lobules— modifications that I have not 

 been able to verify. 



M. Van Beneden's brief remark on the proboscis in Polia involuta has already 

 been adverted to. It may also be stated, however, that, in addition to the in- 

 completeness of his figure, he represents certain lines,* which indicate a sheath (one 

 of his culs-de-sac) around the proboscis — a state that has not been seen in our 

 examples. The structure of the stylet-region, as observed by him in Polia obscura 

 (Tetrastemma varicolor ?), is erroneous. He represents no ducts to the lateral 

 stylet-sacs; no ejaculatory duct. The division of the reservoir has a cavity in 

 the centre, but is likewise furnished with two hypothetical oval vesicles or cavi- 

 ties, and the muscular structure, the floor or ending of the anterior chamber, and 

 other important points, are absent. The statement, that the lateral stylet- sacs 

 contained stylets of a smaller size than the central, and of a different form at 

 the base, shows the learned author did not possess good opportunities for 

 examining these creatures. He follows Dr Schultze in calling the lateral sacs 

 pouches of replacement, and therefore is not aware of the true physiology of the 

 parts. While he states that the proboscis is enclosed in a separate sheath, he 

 distinctly adds, that its muscular retractor is attached to the skin of the animal 

 posteriorly; and that there may be no misunderstanding on the question, he 

 again repeats the statement when drawing up his conclusions, by erroneously 

 averring that the internal surface of the proboscis is ciliated, and that it is fixed 

 to the bottom of the digestive tube by a retractor muscle, as in the stomach of 

 the Bryozoa. f 



Prof. Keferstein's^: remarks, so far as they go, upon this region in Polia man- 

 dilla, are decidedly in advance of his predecessors. He, however, does not men- 

 tion the minute glands on the floor of the anterior chamber, and shows the 

 central aperture for the stylet in the same by far too large, so that in extrusion 

 the muscular space (e in our figures) becomes obliterated. The muscular setting 

 of the granular sac is also continued too far forwards in his figure. He indicates 

 no oblique fibres from the pit of the anterior region (as shown in Plate IX. 

 fig. 3), and the thick coat of the reservoir is described as composed of longitudinal 

 fibres. The external granular glands are not distinctly described ; and the dis- 

 proportion between the central and lateral stylets is so great, that I fear some 



* Mem. de l'Acad. Roy. des Sc. de Belgique, torn, xxxii. pi. iii. fig. 7. 



f Op. cit. p. 44. Unfortunately this author has not lettered his plates, so that I have often 

 been at a loss as to his interpretation of structures of which no mention is made in the text. 

 t Zeitsch. fur wiss. Zool. Bd. xii. p. 72, taf. v. fig. 4. 

 VOL. XXV. PART II. 4 T 



