88 ART. 4. — N. YATSU : 



and are, therefore, much smaller than in the adult. As far as 

 their origin is concerned, they are produced between the peri- 

 toneum and the outer ectoblast of both the dorsal and the ventral 

 walls of the body cavity. As they have a great affinity for 

 erythrosin it is not difficult to detect them in sections. As to 

 the formation of the spindle bodies the reader is referred to my 

 paper on the histology of Lingula (loc. cit.). 



Alimentary canal. — No noticeable change occurs during the 

 stage of sedentary larvœ which I was able to study, except that 

 the constriction of the liver lobes has become a little more 

 marked. The posterior cœca of the ventral lobe of the liver show 

 a greater increase in length posteriorly than in the preceding 

 stages (PI. VIII., Fig. 128). We can now therefore notice four 

 cœca, two dorsal and two ventral, occurring in the same trans- 

 verse section. In some larvœ the pit at the bottom of the 

 mid-gut is still visible. 



Mesenteries. — The mesenteries show but minor chances from 

 the conditions of the preceding stage. The only one which 

 requires special description is a portion of the ileo-parietal band 

 which is situated at the entrance of the peduncular cavity. This 

 portion of the mesentery elongates to become connected with the 

 intestinal mesentery as is seen in the adult. 



Nephridia. — The nephridia are more conspicuous in this than 

 in the 7-9 p. c. stage. They are readily seen as a pair of 

 moderately thick strands filled with refractile excretion granules ; 

 mixed with them oil globules are found, being blackened in the 

 osmic preparations (PL VI., Figs. 86, 87, and PI. VIII., Fig. 



