ON LARVAE OF LINGULA AND PELAGODISCUS (DISCINISCA). 69 



Fig. 16. Proximal portion (about two-fifths) of one of the three jointed chsetse in the ventral mantle-fold. 

 Seep. 61. (x800.) 



Fig. 17. Sagittal section of a larva. Note that at the margins of the shell-valves the periostracum is 

 turned in and continued for some distance over the mantle-fold. The surface of the periostracum is studded 

 with minute points and is therefore shown dotted. The mantle is in contact with the inner surface of the 

 shell, and, except over the body proper, is composed of two lamella?; these are represented diagrammatieally 

 as two thin nucleated membranes, over the greater part of its area the mantle is very thin. See pp. 61-65. 

 (x450.) 



Fig. 18. Horizontal section of a larva passing through the middle of the pigment spot ("eye"), and 

 through the sfcatocyst of the right side. A portion of the outline of the right anterior occlusor muscle is 

 shown by dotted lines. See pp. 63, 64. ( X 700.) 



Fig. 19. Three cells from the postero-ventral wall of the mid-gut, i.e. cells of the future stomach. 

 See p. 64. (xlSOO.) 



TRANS. ROY. SOC. EDIN., VOL. LI, PART I (NO. 3). 11 



