of the Fishery Board for Scotland. 



247 



are inserted into the skin in rows, which, when the skin is separated, 

 show as ridges (fig. 39). The space between these ridges is occupied by 

 glands (g). 



The large white glandular area surrounding the groove on three sides is 

 that which was indicated on the outside of the foot by the yellow band. 

 When cut into there issued a copious, finely granular fluid that coagulates 

 soon. The white gland is laminated in structure, although its connective 

 tissue seems practically solid. It teazes into stringy material. Muscles 

 run longitudinally through the white gland (m, fig. 51). Next the side 

 of the groove a part of the glandular area is distinguished from the 

 rest by a slight difference of colour. It consists apparently largely of 

 oblique muscular fibres with glandular tissue (m and g). The longitu- 

 dinal muscles of the foot give off fibres to the glandular area. The skin 

 at the lip of the groove is thin and is connected by fibres to the white gland. 



The Muscles. — Between the large glands and the skin are the 

 longitudinal muscle bundles, inserted into the skin and giving off fibres to 

 the glandular parts. 'I here are also oblique muscles on either side of 

 the lip of the groove (m and g). Associated with them can be seen 

 some violet pigment. 



The longitudinal muscles consist of two main median muscles and a 

 lateral on either side. Large lacunas are to be seen opening between 

 the muscle bundles. There are glands associated with the muscle 

 bundles and fibres 



The Vessels. — The median vessel occupies a position between the two 

 median groups of muscles, and is flanked also by the so-called green 

 glands. This vessel opens to the depression at the end of the groove, as 

 Sabatier maintained. It continues past the opening for a little distance 

 into the tip of the foot. Each lateral vessel is associated with a lateral 

 muscle. 



Green or Purple Gland — The green (or purple) gland is situated 

 above the main glandular area. There are muscles in this gland. An 

 apparent vessel which was noted by Tullberg was also seen. It was 

 dark violet in colour, and showed its centre a deep violet. The muscles 

 of the gland are inserted in sheaths into the lower surface of the foot 

 beyond the white glands. This gland is much bigger than the white 

 gland near the end depression of the groove. The glandular tissue next 

 the gland is mottled lightly violet, and the muscle fibres have a slight 

 violet tinge. Fig. 55 shows an element-of the purple gland. 



The Groove. — I found no cilia in the groove. In the section I saw 

 a hair sticking out from the side, but it appeared to be merely a thread 

 of the secretion, which had taken the shape of the opening of the duct 

 from which it issued. The secreting region in section shows a mass of 

 little tubes (sees, fig. 55). The cushion lips show an outside cuticle. 



Longitudinal Section. 



In longitudinal section it is seen that the muscles gradually taper from 

 the proximal part to the distal ; that is due to the fibres being gradually 

 inserted into the skin. 



The white gland is seen to be smaller in the proximal part than 

 distally. 



The Byssus Pit. 



The byssus issues from the proximal extremity of the groove in the 

 foot. If the byssus pit and the foot be dissected away from the remainder 

 of the mussel the relationship of the parts is more readily seen. (Figs. 

 45 and 60.) 



