No. 6.] 



PHOKOXIS PA CIF1 CA. 



287 



The ciliated ridge was present for a considerable distance in 

 the oesophagus, but could not be seen in the stomach either as 

 a ridge or a groove. In Figs. 2, 4 it is indicated in section, 

 where it appears to be a shallow groove, an appearance probably 

 due to the folding of the wall of the oesophagus. Its position 

 relative to the longitudinal blood vessels is identical with that 

 described for /'. arcJiitecta. The nuclei stain more intensely 

 with haematoxylin than the other 

 nuclei of the oesophagus, and are 

 crowded together usually in several 

 layers. These facts make the area 

 quite conspicuous in section. 



The muscles reach their greatest 

 development in the oral third of 

 the body, where they form more 

 than eighty high narrow ridges. In 

 the aboral third these are reduced 



. FIG. 5. Semi-diagrammatic cross-section 



to a very inconspicuous layer, though uf i oph0 phore organ within the 



still retaining their identity, being ity of the lophophore. 

 separated throughout their length by characteristic folds of 

 peritoneal epithelium. 



There is a delicate peritoneum covering the muscle ridges, 

 the nuclei only (Fig. 3, ;/) being seen with ordinary powers of 

 magnification. Occasionally a similar nucleus is found within 

 the fold of muscle (;/'). 



The nervous system is constructed as in P. arcJiitecta, with 

 one interesting exception. The two longitudinal cords, which 

 are of exceedingly unequal length, instead of ending in the 

 nerve ring of the lophophore, are continuous across the median 

 line at the level of the median mass of ganglion cells. The 

 loop thus formed is closely applied posteriorly to the latter and 

 .touches the lophophore nerve on each side of the rectum, appar- 

 ently without fusing at either point. Just how intimate this 

 contact is cannot be determined from my poorly fixed material. 

 The brevity of the descriptions of this portion of the nervous 

 system in P. architecta and other species leads me to suspect 

 that the seemingly exceptional condition in P. pacifica may 

 prove to be of more general occurrence. 



