!36 POLYMNIA NEBULOSA. 



Montagu's description (1818) is characteristic, and in his examples the branchiae 

 were likewise speckled with white. His specimens from Devonshire appear to have 

 been about the size of those from the Outer Hebrides, viz., 6 or 7 inches and I inch 

 in diameter. He thought the ventral shields were dorsal. The example figured had 

 a reproduced tail. He describes the tube as composed of slimy matter covered with 

 gravel and broken shells. 



Dalyell (1853) procured his examples from Shetland. He gives no details of 

 structure, though seventeen pairs of bristle-bundles are represented in his plate. He 

 noted regeneration of the posterior extremity, the new region being grey at first, but 

 gradually darkening and becoming finely speckled in five months. 



Claparede (1868) had doubts about the identity of Terebella Meckelii, Belle Chiaje, 

 and T. nebulosa of Montagu, but the differences in size (the northern form being much 

 larger) and the colour of the tentacles cannot be depended on, and so far as can be 

 judged these forms are the same. He draws special attention to the rounded gland- 

 capsules in the pads or tori for the hooks, and considers them peculiar to the species. 



Salensky (1883) gives a careful account of Terebella Meckelii with excellent figures. 

 He describes the various stages, and the derivation of the various organs from the 

 epiblast, mesoblast and hypoblast (his entoderme). 



The Terebella viridis, n.s. of Malm 1 (1872), has three thinly branched branchiae 

 somewhat after the condition in Nicolea, and is held to be a variety of the present form. 



De St. Joseph (1894) describes six segmental organs, two small in the third and 

 fourth segments, a third in the fifth, and the last three in the sixth, seventh and eighth 

 segments. He found an encysted Distome in this species anteriorly. He does not allude 

 to any commensalistic form in its tube. This author 3 (1906) found many specimens 

 of the G-regarine DoUocystis, some free without the epimerite, others fixed by the latter 

 to the wall of the intestine and having posteriorly a diaphanous membrane. He also 

 records Gregarines of the genus Ulivina, Ming. (Syria, Leger), and of the genus 

 S el e iridium, free stages of Gregarina terebellse of Kolliker. 



Paton 3 (1899) describes the heart-body in Polymnia as a cylindrical rod over which 

 the blood flows on its way to the gills, and attached to the wall of the heart by fine 

 processes. It is mesoblastic in origin in this form, and, as Eisig suggests, it may 

 be of the nature of intra-chloragogen, or modified peritoneal tissue, since " the tissues 

 included under that designation " differ chemically. The heart-body being situated in 

 the stream of blood from the alimentary to the respiratory organs, Paton concludes that 

 its functions may be similar to the liver of the higher forms. 



Fauvel considers the small Terebella Grubei procured by the " Challenger " in 

 Australian waters this species, and the hooks certainly show little difference. 



In the British Museum preparation 62.5.7.43 (labelled T. conchilega) is Polymnia 

 nebulosa from Polperro, where it lives in chinks of rocks. 



1 l Annul. Goteb./ p. 97, Tab. i, fig. 7. 



2 c Ann. Sc. hat./ 9 e ser., t. iii, p. 176, pi. hi, fig. 56. 



3 l Quart. Journ. Micros. Sc./ vol. xli, p. 288, pi. xxi, figs. 33, 35 and 36. 



