986 MR. F. A. POLTS ON 
hidden by the peristomial appendages, which are here small 
and slender objects. The peristomium forms a well-developed 
funnel. In P. prolifica, on, the other hand, though I have 
examined a large number of individuals, I have experienced 
considerable difficulty in making out the relations of the pro- 
and peristomium. J think it is possible to say that the pro- 
stomium is smaller, and less definite than in P. anglica, and that 
the peristomial appendages are quite minute, and do not cover 
the eyes. The peristomial funnel is complete. 
I have been able to examine two of the species described by 
Mr. Crossland, and preserved in the Museum of Zoology at 
Cambridge, to test the variation which occurs in the different 
species of Phyllochcetopterus. In P. elioti from Zanzibar the 
pevistomial appendages are compa atively large and definite 
structures, though they do not cover the eyes, the prostomium 
is much better developed than in P. anglica aud P prolifica, 
but the peristomial funnel completes little more than a semicircle 
(Crossland, 2, pl. xiv. fig. 1). 
Text-figure 9. 
Phyllochetopterus anglica. 
Dorsal view of head and anterior segments. 
In P. pictus, also from the neighbourhood of Zanzibar, the 
prostomium is rather large and fleshy, and the peristomium does 
not form a funnel but a conical elevation, divided behind by a 
median groove; the mouth is a small slit-like aperture. In 
another species P. aciculigerus described by Crossland, the 
peristomium is very much reduced, forming a cone with a rounded 
mouth. The prostomium is small, but definite. 
From the small series of species here examined, I have 
ventured to draw some conclusions. The prostomium is always 
a very definite organ, except in a species like P. prolifica, where 
the peristomial collar is quite complete. The peristomium, 
however, varies a good deal. In P. pictus and aciculigerus it 1s 
small and rudimentary, while in other forms it is developed intoa 
funnel—markedly incomplete, for instance, in P. elioti, less 
so in P. anglica. With the completion of the peristomial 
funnel in Mesochetopterus taylort and Chetopterus we have the 
suppression of the prostomium and the complete disappearance 
of the peristomial appendages. I think that the conical peri- 
stomium is primitive and that the formation of the peristomial 
funnel is a direct adaptation to microphagous habits. 
