44 



(PI. II., fig. 8, ret.) of peculiar characters. This tissue 

 which, in the ripe Mussel, was represented by a few 

 delicate fibres, lying wedged in between the tubules, has 

 now increased greatly in mass, and occupies almost the 

 whole thickness of the mantle lobes. It does not, like the 

 corresponding tissue in the Oyster, consist of cubical or 

 polygonal cells, with clear bodies arranged to form a 

 coarse network, the bars of which are composed of distinct 

 cells, but is rather a syncytium, in which cell outlines 

 cannot be readily distinguished. The surfaces of attach- 

 ment of the parts to each other are large, but occasionally 

 delicate fibrous connecting strands may be found. The 

 cells are multinucleated, an isolated patch may be seen to 

 possess several nuclei, but no trace of cell walls. The cell 

 substance stains deeply with eosin. In moderately thick 

 sections it appears to be dotted over with small, light, 

 circular areas, but in thinner parts these are seen to be 

 vacuoles, possibly filled with a substance which does not 

 readily stain. 



The epidermis (PI. 11. , fig. 3, ep. ext.) of the mantle is 

 formed of a single layer of cells, with large nuclei and 

 rather indistinct cell walls. On the internal face of the 

 mantle this epidermis is ciliated. Beneath it there may 

 be a layer of longitudinal fibrous tissue, but this is not 

 constantly present. The reticular tissue of the interior 

 of the mantle is connected with the epidermal layer by 

 delicate strands, but occasionally large rounded masses 

 may be seen lying beneath the former. The epidermis 

 contains eosinophilous cells forming projections internally 

 and externally. Blood vessels are abundant along the 

 external face of the mantle (PI. II., fig. 4, hi. sp.). The 

 larger of these have a fine endothelial lining the structure 

 of which is difficult to make out. These, as well as the 

 interspaces of the reticulum beneath the epidermis, may 

 be crowded with blood corpuscles. 



