HEART-BODY, ETC., OF CERTAIN POLYCH^TA. 273 



it very difficult to distinguish the cell walls. On examination 

 with an oil immersion, however, a framework of cells is seen to 

 support the granules (fig. 11), some of which are enclosed in 

 these medullary cells, whilst others appear to be intercellular. 

 The granules are greenish yellow in fresh tissue; in sections they 

 remain unstained with hsematein, and are of a bright yellow 

 colour. They very frequently occur in heaps, constituting 

 larger granules {b). Occasionally a granule may be noticed 

 set in a vacuole (fig. 5, a). Besides these there are large 

 homogeneous granules, often kidney-shaped, which stain in- 

 tensely with Ehrlich''s hsematein.^ 



There still remain to be mentioned the most remarkable 

 structures in the heart-body of this worm, and which, on 

 first looking at a section of the organ through a microscope, at 

 once arrest the attention by their striking appearance. 



The medullary tissue contains numerous spherical cavities 

 (figs. 2 and 5), the majority of which are occupied by from one 

 to eight round or oat-shaped bodies. In those which are round 

 a " nucleus " is frequently well marked ; and were it not for 

 their large size, which gives them a resemblance to ova, and 

 the fact that the " nucleus " is the only spot staiuable with most 

 dyes, there would be little need for hesitation in pronouncing 

 them to be single cells. Those which are oval in shape are 

 much creased and folded ; they stain irregularly with Ehrlich's 

 hsematein or with fuchsin, some folds colouring intensely, others 

 hardly at all. Picric acid, used after haematein, stains the 

 blood, and also stains parts of these bodies ; but eosin, which 

 likewise stains the blood, does not aff"ect them. 



Some of the spherical spaces are empty, whilst others again 

 contain a colourless refringent, unstainable mass, dotted with 

 numerous dark points. The mass does not quite fill the cavity, 

 but the remaining space is partially occupied by a fine crumpled 

 membrane which appears to ensheathe the colourless bodies. 

 Smaller masses of the same unstainable material are seen in 

 some sections embedded in the groundwork of the organ. 



1 I.e. Ehrlicli's bsematoxylin, with the substitution of haemateiii for 

 hseniatoxjlin, as Majer recommends for all cases. 



