536 I. IKEDA : 



TJie prcoral lube. This is u .structure wliicli looks like ;i 

 broad liood with its concavity directed downwards. It almost 

 entirely covers the upper anterior part of the collar/" when not 

 influenced ])y external circumstances. Masïer.aeax has made the 

 statement that in its natural attitude the hood has its leuii'th 

 disposed parallel to the ]>rincipal 1)ody-axis. However, if the 

 larva be examined in the living state, it will at once l>e discovered 

 that its normal disposition is horizontal. It l)ecomes turned up 

 only as the result of preservation. Its whole surface is covered 

 with cilia, most strongly developed along the free margin which 

 constitutes the preoral ciliated belt. In the full grown larva, the 

 ganglion (and also the sensory spot in ty[)e B) has also a set of 

 sjK'cially long cilia on the outside. Numerous line and refractive 

 ]ierve fibres are seen radiating from the ganglion {gl.) to the free 

 margin of the lobe {pre. hel.) (figs, 13 and 14). 



Masterman has described and figured two ectoblastie struct- 

 ures which are said to be situated on the ventral wall of the hood 

 and which he has named the " oral " and the " pharyngeal " 

 grooves. These he compares, as to their function, to the gill- 

 slits of the Chordata. I can not but think that that writer has 

 liere fallen into a very grave error, which might have been 

 avoided, had he examined the structures in question in living 

 specimens. Among the preserved s})ecimens I have fre(piently 

 noticed those in which the lower or oral wall of the hood Avas 

 ])roniinently bulged out in front of the mouth. \i\ consequence 

 of that prominence (iig. IC), j>ro//(.), thei'c was produced on either 



■•'■1 ;i(Uipt tills iKUiie ul' Mastcnnuirs tn ilfimk' lliat portion dftlic I.-irval Ijotly whk'li lichi 

 in iVoiit ui'tlie tt'iUacular circle and bohind the preoi-al Idhe. 



