Fig 1 . 25. Dissoconch Phase 4. View of right valve of scallop about one week 

 after "set." Note contrast between the prodissoconch (pd) or embryonic shell 

 and the succeeding dissoconch growth (d). A groove has been formed by the 

 growth of the byssal or foot notch (bn), which is increasing in size to correspond 

 with the development of the foot. The right valve is smaller than the left. Mag- 

 nified 37 1 /2 diameters. 



Fig. 26. View of left valve of same scallop as in Fig. 25, showing the lines of 

 growth and the formation of the pseudo-ear, which corresponds to the location of 

 the byssal notch. Magnified 37^/2 diameters. 



Fig. 27. Same scallop as in Fig. 25, with foot extended. Anatomy shown 

 through transparent left valve. Note increased number of gill filaments (ig) and 

 the well-defined heart (ht). The byssal gland (bg) and cleft have become promi- 

 nent on foot. The knob-like projections on the mantle are the beginnings of the 

 tentacles (t). Magnified 37 Va diameters. 



Fig. 28. View of soft parts of slightly older scallop of Phase 4. Note the 

 nine small tentacles (t), the two eyes (e) and the fourteen gill filaments (ig). Mag- 

 nified 37 l /2 diameters. 



Fig. 29. Dissoconch Phase 5. Anatomy shown through transparent right 

 valve. This stage is characterized by one tooth in the byssal notch. The scallop 

 is represented as lying in a resting position, with mantle and foot retracted. Note 

 the formation of eight secondary tentacles between the primary, the relative posi- 

 tion of the eyes (e) and the tenatcles (t), and the beginning of the outer gills (og). 

 Magnified 37 1 /2 diameters. 



Fig. 30. View of same scallop as shown in Fig. 29, as seen through left valve, 

 with mantle (m) expanded and foot (f) extended. The edges of the mantle have 

 joined posteriorly to form a pseudo-siphon (ps), through which water is expelled 

 from the shell. The byssal gland (bg) has a prominent position on the long foot 

 (f). Magnified 37 l /2 diameters. 



Fig. 31. Dissoconch Phase 6. Characterized by two teeth on the byssal 

 notch. View of anatomy through right valve. Tertiary tentacles are developing 

 on the edge of the mantle, which is partially extended. At this age the scallop 

 has about twenty-two inner (ig) and ten outer (og) gill filaments. Magnified 37% 

 diameters. 



Fig. 32. Scallop of same phase as in Fig. 31, lying on left valve in an unnatural 

 position. The animal has extended his foot (f) for the purpose of turning over. 

 The eyes (e), tentacles (t) and guard flap (mf) can be seen on the edge of the mantle. 

 Magnified 37 1 /2 diameters. 



