ON THE DEVELOPMENT OF LINGULA ANATINA. öö 



example, attain almost the normal size of those of the 12-13 

 p. c. stage ; while the larva? at the 15 p. e. stage when imperfectly 

 nourished would not exceed in size well-fed larva? of the 8-9 p. c. 

 stage. 



VIII. STAGE OF 3 PAIRS OF CIRRI. 

 (PROTEGULUM STAGE.) 



During the past three seasons (1899-1901) the larva? of this 

 stage were found in tow-nets only on one occasion (July 28 = 21 

 of the lunar calendar). The larva?, as far as I could judge from 

 my experience, were five or six days old. This being the case, 

 the eggs must have been laid at the preceding spring tide. As 

 Lingula in confinement laid eggs on July 27, there is a good 

 reason to believe that in captivity spawning was delayed for 

 about five days by the unnatural conditions of confinement. 



On the single occasion when the larva? of this stage were 

 collected, there were unfortunately so few of them that I was 

 not able to obtain satisfactory sections. I shall, therefore, refer 

 chiefly to the structures which could be determined in surface 

 view. 



The larva? at the stage (PI. V., Figs. 73, 74.) differ but 

 little from the oldest of those I succeeded in rearing from the 

 egg, and thus there is fortunately no gap in the materials ob- 

 tained from the two sources. In the larva? under consideration 

 the most striking feature is the great increase in size of both the 

 mantle and the shell. The latter attains the typical form of the 

 Protegulum, as defined by Beecher, ('91 p. 344). It is a little 

 higher than a semicircle, the ratio of the height to the length of 

 the posterior edge, being 3 : 5. The posterior straight edge, 



