NO. 8 THE POLYCHAET — RAW 27 



different from that of Racovitza. In his view the peristome did not 

 differ fundamentally from a normal segment (1896, p. 154) ; the 

 head of the ancestor became the head of the polychaet; the parts 

 were already there, including the primal elements of the cerebral 

 nervous system — the "aire palpaire," "aire sincipitale," and "aire 

 nucale." Only further development of these was needed: that of 

 the sense organs on them into palps, antennae, eyes, and nuchal 

 organs; that of the areas themselves into the fore-, mid-, and hind- 

 brains. Before this evolution in the polychaet there were no com- 

 parable sensory organs (1896, p. 161). On the contrary, according 

 to the theory here presented, the ancestor was already furnished with 

 eyes and parapodia throughout the body, and possibly also some form 

 of appendages and eyes on the head, which already possessed a brain 

 and bore also an early stage of the mouth-lips. The 4 (or more) pairs 

 of ganglia, too, which initiated the mid- and hind-brains were already 

 functioning in their own postcephalic segments. But whatever sense 

 organs that primitive annelid had on its head, except for the mouth- 

 lips these organs were superseded in the evolution of the polychaet by 

 previously postcephalic eyes and antennae ; while its brain was to be 

 extensively supplemented and partially superseded. A fundamental 

 difference between the two views is that Racovitza in evolving the 

 polychaet brain thought he was evolving that of the primitive annelid, 

 whereas on the here offered theory no primitive annelids survive. 



APPLICATION OF THE AUTHOR'S THEORY TO POLYCHAETS 

 IN GENERAL 



Very close comparisons are now possible between the different 

 families of errant polychaets in regard to the prostomium and its 

 appendages and eyes, the brain, the stomodeum, and the central and 

 visceral nervous system; and, to judge from the results of past re- 

 search, the suggestions of close affinity are not likely to be diminished 

 in the future. In the accompanying table typical representative sub- 

 orders and families are tabulated in regard to their brain, sense organs, 

 stomodeum, and buccal segments ; in it, too, the homologies are 

 indicated, and characterized as succinctly as possible. The agree- 

 ment in brain and sense organs is extremely close; and even in the 

 stomodeum, though the characteristics vary so much, a series of 

 stages can be seen between the Eunicimorph through the Amphino- 

 morph to even the Glycerimorph. 



In table 3 the order of development of the different sections of 

 the stomodeum is to some extent indicated by the letters a, b, c ; and 

 the order of incorporation of the divisions of the brain by A; BI, 

 BII, Bill; C 



