NO. 8 THE POLYCHAET — RAW 



ABBREVIATIONS USED ON FIGURES 1-5 



The central nervous system is in outline, the visceral nervous system is in 

 black in figs. 4 and 5. 



(h, nerve of the posterior single antenna. | 02, nerve of the posterior pair of 

 antennae. ] as, nerve of the anterior part of antennae. 



b, bearer. | bfj fore-brain. | bmi, anterior section of mid-brain. | bm2, Heider's 

 hind section of mid-brain. | bh, hind-brain. 



ch, chitin thickening on the base of the prostomium. | cl, callus on the jaw- 

 pad. I CO, buccal commissure. 



d, dissepiment. | ec, ectoderm. | onlj epithelium of the mouth-lips. 



/, fang, fp, fore pad = / //. 



gi, supra-oesophageal ganglion of visceral nervous system. | ^2, infra-oesaopha- 

 geal ganglion of visceral nervous system. | g^, hindmost oesophageal ganglion. 

 I gc, ventral ganglion chain. | gx, x-form ganglion body. | gp, glandular pouch. 



JP, upper jaw pad. | //, lips of pharyngo-oesophageal rift. | III, lips bound- 

 ing the upper jaw sacs. | ////, lip bounding the lower jaw sacs, the lower 

 lip. I //, lower jaw. 



m, muscles of the prostomium. | nig, beginning of mid gut. | mj, muscles of 

 the jaw sac. | ml, dorsal longitudinal muscle. | mr, ring muscle layer. | mrt, 

 retractor of the jaw sac. 



n, oesophageal visceral nerve or nerves (from the fore brain). \ n co i, 

 oesophageal visceral commissure, anterior part. | n co 2, ditto, posterior part; 

 in figure 4 it is the inner pair joining in g-i', the outer pair is n oe I, following. 

 I n oe I, lateral oesophageal nerve. [ n ph, pharyngeal visceral nerve | nu, 

 nuchal organ. 



oe, oesophagus. | pi to /'s, podial nerve roots. 



s, saw-plate. | sli, sh, sacs of the lower jaw. ] sui, su2, sacs of the "upper" 

 jaw. I t, "tooth." 



The present author's views as to the evolution of the brain and of the gut 

 are suggested by the order of the capital letters A, B, C (respectively fore-, 

 mid-, and hind-brain), and the Roman figures I, II, and III for the three 

 successive invaginations and the three different ganglion pairs in the mid-brain. 

 The original brain was the fore-brain and the corresponding gut the mid-gut. 

 The first addition to the gut was the oesophagus— I, after which B I was added 

 to the brain. The second addition was the upper jaw series of sacs with their 

 armature — II, after which B II was added to the brain. The third addition 

 was the lower jaw sacs with their armature — III, after which B III was added 

 to the brain; which then incorporated also the hind-brain — C. The sequence of 

 lower lips resulting from the successive invaginations are still represented by 

 / /, / //, and / ///, the present lower lip. The concomitant evolution of the 

 visceral nervous system need not be repeated here. 



