of the Fishery Board for Scotland. 



253 



EXPLANATION OF PLATES. 



PLATE XVI. 



Fig. 1. Two-years old mussel, St. Andrews. March. Nat. size. 

 9.^ ... 



4. 



5. 



6. 



7. 



8. 



9. 

 10. 

 11. 

 12. 

 13. 

 14 



16. 

 17. 

 18. 

 19. 



20. 

 21. 

 22. 

 23. 



24. 

 25. 

 26. 



27. 



28. 

 29. 

 30. 

 31. 

 32. 



33. 



34. 



35. 



36. 

 37. 



38. 



39. 



40. 



41. 



42. 



43. 



U. 

 45. 



Mussel opened to show the relation of the foot (f) and byssus (by). 

 Three-years old mussel, St, AndreAvs. March. Nat. size. 



,, M 5> )> 5> >> 



Ripe Egg of Faroe mussel, Cam. luc. Obj. DD : Oc. 2, Zeiss. 

 Egg of Faroe mussel. 



,, at 1 p.m., June 3rd. 

 Section of byssus-pit- showing glands (g). 

 Egg of Faroe mussel at 10.30 a.m., June 4. 



Nearly ripe egg of mussel, removed from the mantle. July 1 . 

 Egg of Faroe mussel at 10.30 a.m., June 4. 



and 15. Eggs at 3 p.m. June 3. The yolk contents have beer 



squeezed out, leaving real or apparent nuclei. 

 Unfertilized egg of Faroe mussel : budding. 

 Egg of Faroe mussel at 1 p.m., June 3rd. 



Enlarged drawing of process from the micropyle of the egg shown in 

 Fig. 18. 



Egg of Faroe mussel at 10;30 a.m., June 4. 



Longitudinal section of byssus-pit and foot, showing muscles (m), glands 



(g), septum (sep), groove (gr), byssus (by), foot (f). 

 Sperm of mussel. 



Egg of Faroe mussel at 7 p.m., June 3. 



Bean-shaped slow-growing mussel, which had -been kept for two years 



in Laboratory. Side view. Nat. size. 

 Bean-shaped slow-growing mussel, which had been kept for two years 



in Laboratory, view from above. Nat. size. Compare with Figs. 31 



and 32. 



Egg of Faroe mussel at 3 p.m. June, 3. 



Broad mussel from pond, quick-growing, side view. Nat. size. 



,, ,, ,, view from above. Nat. size. 



Compare with Figs. 26 and 27. 

 Shows the evertible inner collar (i-c and i'c) of the byssus-pit, outer collar 



(o-c), byssus (by). 



Septum from byssus-pit : glands (g). Cam. luc. Obj. a and Oc. 2, Zeiss. 

 Egg of mussel nearly ripe, July. Part of the yolk contents has been 



pressed out. Nucleus (n). 

 Diagrammatic longitudinal section of the film of root of bysus of a 



preserved mussel. 



Byssus-pit and byssus seen from the side. The skin and glands have 



been dissected off, and the edges of the septa exposed. Anterior side 



(ant), posterior side (post), muscle (m), septum (sep). 

 Egg of Faroe mussel at 7 p.m. It has been burst; a "nucleus" 



remains inside the capsule, and a little collection of protoplasm is 



attached to the outside of the zona. 

 Skin of foot seen from inside — showing the longitudinal muscle strands 



(m), and the glands (g) between them. 

 Mussel which had a dark amber-coloured frill to the inhalent aperture 



(in), and a white exhalent aperture (ex). ' 

 An apparent nucleus formed by the union of clear protoplasm and yolk 



granules, both of which had been pressed out of an egg. 

 Groove of foot opened out to show the cushion lips (1), byssus (by), 



byssus-pit (by-p), and depression at end of the groove (de). 

 Mussel that travelled actively by means of its foot (f) along on the 



level. Nat. size. 

 Mussel (female) that spawned. Nat. size. 



Foot of mussel, showing yellow glands (y-g) that border the groove in 

 its whole extent. 



