NOTES ON THE STRUCTURE OF OIKOPLEURA. 43 



right hand end of its dorsal surface. The cells near the 

 aperture of the funnel are very large and distinct while 

 the cilia they bear are long and numerous and lie directed 

 upwards towards the inner end of the funnel. That csecal 

 end is supplied by a nerve. The central nervous system 

 is here at its largest. It shows large granular nerve cells, 

 and the otocyst (PI. IV. fig. 6, o.c). The endostyle and 

 the lateral oral glands are very much as before. 



Ten sections further forward, No. 266 (PL IV. fig. 7) 

 we find the body still smaller. It is now close to the 

 anterior end, and this is the last section we figure. The 

 pharynx is now small and will shortly terminate in the 

 oral aperture. The two large glands lie alongside it, but 

 the endostyle is no longer visible ventrally, we are in front 

 of its anterior end. Dor sally the nervous system is seen 

 attached to the inner surface of the ectoderm, where it 

 extends outwards into two lateral processes. Figure 8 

 shows this region more highly magnified (X 600). The 

 ectoderm is here distinctly two layers thick, and is covered 

 by a cuticle or test which can be traced as a distinct 

 though thin layer completely round the body in this 

 region. 



The nervous system, then, when traced through the 

 whole series of sections is seen to be connected anteriorly 

 with the dorsal ectoderm close to the mouth ; then it 

 becomes free from the ectoderm and expands to form the 

 large ganglionic mass or brain placed above the front of 

 the pharynx (see PI. IV. fig. 9, n.s.) and having two sense 

 organs, the ciliated funnel and the otocyst, connected with 

 it. The ganglion then tapers posteriorly to form a slender 

 nerve cord, the myelon, which runs backw^ards over the 

 pharynx, rather on the right side of the medio-dorsal line 

 (PL III. fig. 3), until it reaches the oesophagus where it 

 turns ventrally and runs down between the pyloric sac 



