178 



SYSTEMATIC ARRANGEMENT 



The mantle advances over the head. The front shelly valve has 

 advanced over the eye (fig. /). The flat tuberculated surface in front 

 of the valves is gradually diminished, and the eighth valve is pro- 

 duced behind the seventh. 



Fig. 95. — Development of (Chiton) Leptochiton cinereus : after Loven. 



a. Embryo in the egg. 



b. Dorsal view of young Chiton, showing the commencement of the divi- 



sions. 

 v. Lateral view of the same. 



d. Dorsal view of young Chiton further advanced, with the seven irregular 



valves deposited in the segments. 



e. The same from beneath, showing the foot, with the eyes on the side of 



the head. 



f. Dorsal view of a still older Chiton, showing the diminished tubercular front 



portion. 



The valves are at first short, with an irregular wavy outline, but 

 they increase in thickness and size by the addition of layers on the 

 under surface ; and as they increase, two deep notches are formed in 

 the front of the outer sides, which are well marked in the adult 

 shells (fig./). 



Loven regards the circle of cirri as analogous to the cirri on the 

 veil of the young of other Gasteropods and Acephala, but in Chiton 

 the veil is not developed into a broad extensile sail, and he com- 

 pares the anterior portion, having the tuft of filaments, to the pear- 

 shaped body which usually carries the flagellum in the marine Ace- 



