ü26 I. IKEDA : 



end. This hollow protu1)er;ince is the riuUmeiit of the intestinal 

 canal of Actinotroeha. In loni^itudinal section it is shown in lig. 

 37 {hiL). 



In lii;'. ol, ]'e])rcsentini;' a sliiihlly o))li(|ne frontal section of 

 a larva of nearly the same stafj;e as that of iig. 0, we see below 

 the |)it-like ne])hndial sac, which is (|uite free from the gnt. The 

 ectoblastic wall of the jjrc.'oral Ljbe is at this stage somewhat 

 uniformly lined with flattened mesohlast cells, while in the cavity 

 heliind the blastopore the mesohlast cells are for the most part 

 freely scattered, though a few^ have already begun to arrange them- 

 selves against the ectoblast laver in this region. In fis;. So, a 

 transverse section through thc^ p(jsterior end of u larva of nearly 

 the same stage, the nephridial pit appears as a single flattened 

 sac {ncp. p.) lying in front of the intestine [i/d.) ; the ectoblastic 

 Avail is internally lined with a few isolated and flattened mesol)last 

 cells. In a slightly nujre advanced stage, the ectoblast behind 

 the blastopore, and in a less complete degree the gut wall 

 also, shows a similar mesoblastic lining, though a few mesohlast 

 cells still remain free, esjiecially in front of the nephridial 

 sac. 



In order to facilitate comparison with the statements of other 

 writers, I will here add a few words on the change of form under- 

 gone l>y the ne])hridial pit. AVhen in a larva slightly older than 

 that of fig. *J, the preoral lol)e and the future intestinal portion of 

 the gut have become considerably elong.ited, the nephridial ])it, 

 which has meanwhile become deeper than l)efore, begins at its 

 inner blind end t(j divide into two latei'al branches. Each of the 

 latter corresponds, as will be fully demonstrated further on, to tlie 

 nephridial canal of Actinotroeha. Fig. o.S, a frontal section of a 

 larva at this stage, shows the Ijifurcation just alluded to. The 



