tie more advanced. Here the mouth is considerably larger than 

 in the last stage and has become a narrow slit. A slight 

 shoulder has developed a little above the equator of the larva, 

 while the aboral end has become conical. There is apparently . 

 a thickening in the supporting membrane at the region of the 

 shoulder, but the opacity of the larva prevents a clear view 

 of it. This shoulder is the beginning of the peristome and 



the part of the animal posterior to it is the proboscis. 

 There has been no invagination during the foiination of the 

 mouth, but it is possible that this proboscis arises by an out- 

 growth of the ectoderm between the mouth and the origin of the 

 septal muscles. This seems the more probable when we remem- 

 ber that one of the few points on which Claus and Goette agree, 

 is in regarding the lining of the proboscis as ectodermal. 



IV. The Ei^Jit Tentacle Stage. 

 The period at which the larvae become attached varies con- 

 siderably, but some larvae that were reared from buds and had 

 recently become fixed, were found to be at a stage not greatly 

 in advance of the last. Figs. 6 and 7. The mouth in these 

 is circular and well opened. The peristome is distinculy 

 formed and is eight angled, the four angles in what we may call 

 the principal radii beir^ somewhat more distinct than the oth- 

 er four. The stem is also distinctly formed, and in it the 



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