PROBOSCIS OF SYLLIDEA 335 
muscle, and their ehief function would seem to be to provide 
a series of ‘ points d’appui ’ for the latter. It may be mentioned 
here that it is largely to the presence of these fibres im transverse 
sections in certain planes that the illusion of regular partitions 
between the rows of striated fibres is due. 
VI. Tur PRovENtRIcCULUS : CHITINOUS PLATES. 
In the interior of the proventriculus towards its anterior 
end is an elaborate structure which has hitherto failed to 
receive the notice which its importance in the mechanism of 
the proboscis seems to demand. It occurs in essentially the 
same form in all the members of the group which I have 
examined for it—not only in the Syllidae and Kusyllidae, 
but in the Hxogoneae and Autolytidae. 
De Saint-Joseph seems to have been the first to direct atten- 
tion to the appearance presented by this structure, though he 
misunderstood its significance. In his description of Ty po- 
syllis alternosetosa, he says, ‘le proventricule, avec 
30 rangées de points gris, qui a a sa partie supérieure un 
anneau chitineux ’, with afoot-note, ‘ Cet anneau, quiseremarque 
souvent chez les Syllidiens, me parait étre la continuation de 
la trompe qui pénétre dans le proventricule’. On the other 
hand, he refers to the same structure in Pterosyllis 
spectabilis as ‘ deux valves cornées’ (pp. 65 or 189). Mala- 
quin (p. 213) gives a much more consistent and complete 
description: ‘Dans la région antérieure de l’organe, |’épithe- 
hum prend un autre aspect, il devient en quelque sorte fibril- 
laire; les cellules en sont trés allongées avec noyau médian 
(Pl. v, fig. 7, Hip. pr.). Cette structure correspond a une disposi- 
tion particuliere, & un épaississement de la cuticule formant 
en avant du proventricule un anneau chitineux. Cet anneau 
chitineux, visible sur le vivant (Pl. iv, A. ch., figs. 1, 2, 8, 4, 5), 
peut surtout s’étudier dans une coupe horizontale du proven- 
tricule (Pl. v, fig. 6). Dans la région antérieure de l’organe 
lépithélium est beaucoup plus épais et les parois se touchent 
au Pétat de repos de maniére a fermer totalement la lumiére. 
