34 ART. 4. — N. YATSU : 



As is seen from the above summary of the developmental 

 processes, the general structural scheme of Lingula has by this 

 stage already been attained. No remarkable metamorphosis takes 

 place after this. It is only upon this scheme that the new organs 

 are gradually built up during the post-embryonal stages which 

 will be dealt with in the ensuing sections. 



As for the points recapitulated above, a comparison of the 

 accompanying diagrams will make my meaning clear. 



B. POST-EMBRYONAL STAGES. 



During the post- embryonal stages new pairs of cirri are 

 constantly added at the base of the tentacle. I will divide the 

 larvae to be described hereafter into several stages according to 

 the number of the cirri, thus : 



Co p. c. stage 1 = Protegulum stage. 

 Free-swimmimg J4 p. c. stage. 

 larvae. J5-G p. c. stage. 



(7-9 p. c. stage. 

 Sedentary lame. {10-15 p. c. stage = larvae with protruded peduncle. 



As development goes on gradually, no sharp lines of de- 

 markation between these stages can, of course, be drawn. But 

 the increase in number of the cirri appears to me to be the 

 point that best indicates the age of the larvae. Their size, for 

 instance, is not a reliable criterion, for that is a function of 

 nutrition both in nature and in confinement. When the food 

 supply is specially abundant the larvae at the 7 p. c. stage, for 



1. p. c. = pairs of cirri. 



