BIGELOW. Development of Lepas. 



PLATE 12. 



Lepas fascicularis. 



The figures in parenthesis following the descriptions refer to corresponding 

 stages of L. anatifera. 



Fig. 111. Horizontal section of sixteen-cell stage. (Compare with Fig. 43.) 



Fig. 112. Sixteen-cell stage viewed from vegetative pole. Fifth cleavage. (Fig. 



46.) 



Fig. 113. Same stage, seen from left side. (Fig. 45.) 

 Fig. 114. Thirty-two-cell stage viewed from animal pole. (Fig. 55.) 

 Fig. 115. Same stage seen from left side. (Fig. 53 ) 

 Fig. 116. Same stage viewed from the vegetative pole. Primary mesoblast 



(rf 5 - 2 ) and entoblast (<f 5<1 ) in fifth cleavage. (Fig. 48.) 

 Fig. 117. Egg in same stage, looking upon the posterior pole. 

 Fig. 118. Sixty-two-cell stage seen from left side. 

 Fig. 119. Same stage. Sagittal optical section seen from left side. Primary 



mesoblasts still in sixth cleavage. (Fig. 56.) 

 Fig. 120. Same stage. Horizontal optical section seen from animal pole. (Fig. 



64.) 

 Fig. 121. Sixty-two cells. Primary mesoblasts have completed sixth cleavage, 



being now four in number (c? 7<5 -c? 7 ' 8 ). Two entoblasts. 

 Fig. 122. Profile of late stage. Formation of dorsal transverse furrows (1, }, 



which mark off the three metameres. Seen from left side. (Fig. 91.) 

 Fig. 123. Somewhat later stage seen from left side. Appearance of a third fur- 

 row superficially subdividing the posterior (mandibular) metamere. 

 Fig. 124. Still later stage seen from left side. Another furrow subdivides the 



anterior (first antennary) metamere. (Fig. 93.) 

 Fig. 125. Dorsal view of same stage showing the longitudinal and transverse 



furrows, which, growing ventrally, fold off the appendages. 

 Fig. 126. Nauplius after development of paired appendages and beginning of the 



labrum. Seen from the left side, ventral being up. 



