532 I. IK EDA : 



witli two paii',^ of ns yet very sliort Inrval tontneles ; this i;^ the 

 most ndvaneed (levelopmental stage to be met with in the em- 

 bryonal masses. Fig. 40 is a median sagittal section of such a. 

 highly advanced larva. Here the a^sophagns (œs.) and the in- 

 testine [hit.], wliicli latter now commnnicates with the exterioi- by 

 the small anns {an.), are highly developed, so that the three parts 

 of the alimentary tract (œsophagns, stomach, and intestine), may 

 be said to l)e almost complete. The JiervO ganglion (fig. 40, (/I.) 

 is well differentiated from the ectoblast of the preoral lol)e, pre- 

 senting itself in section as a ronnd, well marked mass principally 

 composed of nerve fibres. I have l)een nnal)le to ascertain whether 

 a proctodœnm is j'troduced at all, and if so, what j^art of the post- 

 gnt it gives rise to. 



The preoral ])ody-cavity is, at this stage of development, still 

 very incompletely separated from the postoral cavity l)y a few 

 mesoldast cells (fig. 43, '//ic.^\). The nephridial canals (fig. 41, 

 7iep. c.) are now distinctly separated and removed from each other, 

 and are fonnd in a cross section to l)e situated laterally to the 

 intestine {inf.). One on the right-hand side of the above figure is 

 cut through at its extei'ual opening, while on the other side the 

 nephridium is represented by a thick mass of a few ectoldastic 

 cells. This lateral shifting of the nephridia becomes more and 

 more pronounced with the advancement of larxal developmeiit. A 

 slightly advanced state of the nephridia is shown in fig. 42, where 

 the nephridial canals {ncp. c.) are now seen tolerably long and have 

 a wall composed of a single row of cubical cells. It is often observed 

 that some mesol)last cells connect the canals with the splanchnic 

 walls (see the above figure). These cells seem to be the first in- 

 dication of the future collai'-trunk septum. Besides, a certain 

 number of mesenchvmatous cells, which later uudoubtedlv become 



