aboral as Goette says it is in Cotylcrhiza, and we shoula ex- 

 pect the two species to a^ree in this particular. 



The mouth is at first very small and is slightly funnel- 

 shaped. It looks under the microscope like a pin hole in one 

 end of the larva. Fig. 3b. There is no indication at the 

 surface of any invagination of ectoderm to form an ectodermal 

 oesophagus. The larva is, however, so very opaque that one 

 cannot get an optical section of it at this stage. A larva 

 at this stage swimming in a watch glass will every little while 

 decrease in speed and Uhti its anterior end downwards until it 

 strikes the glass. Its forward motion will then cease and it 

 will for a short time remain attached to the glass, revolving 

 very slowly on its Ion,?; axis with its oral end tuiTied upwajxi. 

 One may at such a time look down through the mouth into the 

 entoder-mal cavity. After a little, the revolutions increase 

 in frequency, and the larva turns over on to its side, and 

 swims off. So fcir, then, as I was able to observe, there is 

 a free passage from the enteric cavity to the exterior at the 

 time of the first appearance of oral structures and there is 

 apparently no previous invagination of ectoder-m. 



Soon after this, a slight circular concavity appears sur- 

 rounding the oral region in such a way as to faintly outline 

 I the proboscis. Fig. 4a and b. Fig. 5 shows a larva a lit- 



- 30 



