NO, 8 THE POLYCHAET — RAW 9 



and hind-brain — into four divisions, grouped above in two categories 

 (Hanstrom, 1928, pp. 259, 260), and the grading of the three divi- 

 sions of our mid-brain by posteriorly diminishing size is very diffi- 

 cult to imagine; whereas on the theory detailed below it follows 

 quite naturally. 



THE STOMODEUM IN EUNICE AND OTHER POLYCHAETS 



At the outset in this paper the Eunicimorpha have been claimed as 

 primitive, but it may be thought by some that in respect of their stomo- 

 deum they are less primitive than some others. Hempelmann (1934, 

 hi Kiikenthal and Krumbach, Handb. Zool., vol. 2, 7, p. 161, Anne- 

 lida Polychaeta systematic section) divides the Polychaeta Errantia 

 into — (i) suborder Amphinomorpha with tetraneury; and (2) sub- 

 order Nereimorpha with dineury, of which the first family described 

 is the Aphroditidae and the last the Eunicidae. From this one might 

 think that he regarded the Aphroditidae as the most primintive and 

 the Eunicidae as the most specialized. When, however, we note that 

 the systematic part is a translation of Fauvel in Fauvel's order, except 

 for the extraction of the Amphinomidae and its elevation into a sub- 

 order, we may conclude perhaps that the order was without signifi- 

 cance for Hempelmann. 



The stomodeum of the Eunicimorpha is unique among errant poly- 

 chaets — in its form, its armature, and its very slight protrusibility. 

 Its form is remarkable, consisting of the pharynx subdivided into 

 four successive sacs separated by foldings of the pharynx wall, 

 followed by the cylindrical "oesophagus." All the sacs, and the 

 oesophagus as well, extensively communicate with one another by 

 rifts in the midline. The armature, too, is remarkable and of great 

 variety within the suborder; but by comparisons between the various 

 types the courses of evolution can be clearly seen. The denticles are 

 arranged within and on the ventral sides of two of the sacs in all 

 forms, constituting respectively an upper jaw series of pairs of 

 denticles and a lower jaw with a single (chisel and crusher) pair. The 

 evolution of the armature could form a separate paper. In Eunice 

 only the lower jaw chisels and the upper jaw fangs are protruded. 

 The primitive symmetrical pairing of the denticles, well seen in 

 Stauronereis (Staurocephahis) , has been lost in the Eunicidae, s.s. 



In the Amphinomorpha the stomodeum, though very different, 

 presents the nearest approach to that of the Eunicimorpha in the very 

 small amount of its protrusion and in the fact that this is largely 

 limited to the ventral side, recalling the condition in Eunice where 



