ON THE DEVELOPMENT OF LINGULA ANATINA. 85 



XI. STAGE OF 10-15 PAIRS OF CIRRI. 

 (SEDENTARY LARVAE). 



In the foregoing chapter we have discussed in some detail 

 the anatomy and histology of the free-swimming larvae (the 5-9 

 p. c. stage). We will next describe the developmental changes 

 which take place in the sedentary larvae (the 10-15 p. c. stage). 



On keeping the larvae of the 7-9 p. c. stage in a vessel for 

 several days we find that they cease to swim about and attach 

 themselves to the bottom of the vessel by the tip of the protruded 

 peduncle. The larvae assume a vertical position and move their 

 valves laterally against each other with a somewhat gliding motion 

 as in the adult. The attachment of the peduncle is now so 

 firm that the larvae cannot be displaced by even a tolerably 

 severe jerk. From this stage onward, therefore, the water of the 

 vessel may be changed without danger of losing specimens. 

 The protrusion of the peduncle takes place in captivity at the 

 beginning of the 10 p. c. stage, and immediately thereafter the 

 larvae secure their attachment, but at what stage the peduncle 

 is extended from the shell under natural conditions, I was not 

 able to determine. Acceleration or retardation may easily occur in 

 confinement. According to my observations, it took about one 

 month and a half from the outset of development for the larvae 

 to attain the 15 p. c. stage. 



Shell. — The shell increases in length and thickness in the 

 same manner as in the preceding stages. At the 15 p. c. stage 

 it assumes the shape of an ellipse, the ratio of the length to 

 the hinge line being 3 : 1 (PI. VI., Figs. 86, 87). A larva 

 drawn in Fig. 86 (PI. VI.) measures 800/^ in length and 636 /* 



