136 A. OKA. 



tliiiiiier a.s tlic entire j^anglion iiicieiise« iu size. The two exceplional 

 points just referretl to, are wliere the sae-wall produces a pair of solid 

 liorn-like processes, each of which gradually elongates towards tlie ti[) 

 of the lophophoral arms, passing between the two layers of their ceil- 

 ing. The position of the lophophoral nerve-trunks directly beneath 

 the outer layer led me at first to assume their origin from the latter, 

 in a way anrdogoiis to the development of the central nervous system 

 in \ertebrates. A careful study, howevei-, convinced me that such is 

 not the case. 



At the time when the intestinal cavit)' becomes continuous with 

 the exterior at the anus, the whole body-cavity is still tilled up with 

 the ü'ranular mass. Some of the cells of the latter are seen to ditfe- 

 rentiate themselves from the rest, at two regions as seen in a median 

 sagittal section (fig. 51, PI. XX.), the one extendiug between the 

 involuted tentacular sheath and the cystidnl wall, and the other be- 

 tween the lower part of the oral side of the oesophagus and the part of 

 the cystidal wall opposite to it. At these places, the cells lose their 

 granules, elongate, and become spindle-shaped joining the two pointas 

 between which they lie. Their further development has been already 

 treated under the muscular system. The muscles that develope in 

 the above mentioned regions are the pariet(j- vaginal and the retractors 

 of the adult polypide respectively. The muscular layer of the endo- 

 cyst and the alimentary canal developes itself later, prob:djiy from the 

 cells of the lining e[>ithelium in a similar way. 



Almost sinuiltaneously with the first appearance of nuiscles, the 

 cells of the granular mass lying between the blind end of the stomach 

 and the coenoecial wall opposite to it, lose a porticjn of their granides, 

 and aggregate into a solid rod, which is, in sections of stained speci- 

 mens, readily recognizable on account of the deeper coloring of its 

 cells in contrast with the surrounding faintly colored granules. 



