Clisetoptcviis Variopedatiis. 519 



lateral angles of the inoutli (Fig. 12). They extend dorsalwards 

 towards the eyes and bases of the tentacles when it is extended for- 

 wards. These continue to enlarge until they coyer the eyes and the 

 base of the tentacles like in the adult. The post-oral lobe is very 

 contractile, but its lateral edge is usually curved more or less so that 

 the concave side is turned ventralwards when the lobe is flexed, or 

 dorsalwards when extended. This surface is covered with cilia that 

 extend inward and are continuous with those of the gullet. 



The tentacles are not so long as the pre-oral lobe. They are 

 directed backwards, like the very much longer ones which are devel- 

 oped earlier in the related genus, Spioch?etopterus (Text-figure D). 



The five eye-spots, one of which was mesial in position, in the 

 specimen from which Figs. 11 to 13 were drawn, suggests a fusion 

 of the median pair. An individual of the same stage, or slightly 

 older, had a single pair of eye-spots as in the adult. I w^as unable 

 to determine whether the reduction is brought about through fusion 

 or resorption or whether this was the number originally formed. 



A shallow ciliated furrow extends, on the mid-dorsal side of the 

 anterior region, from the anterior convex surface of the pre-oral 

 lobe to the foremost ciliated ring. It increases rapidly in depth after 

 the larva forms its tube, and is well developed in a transformed larva, 

 with four sexual segments, as in any of the mature worms. 



Middle region. — This region includes five segments. The fore- 

 most two bear the ciliated rings and are of greater diameter than the 

 remaining ones which decrease in size regiilarly backwards. The 

 whole region is very contractile and its segments may telescope into 

 one another. 



The foremost segment of this region, which becomes the "twelfth 

 segment in the adult," bears an incomplete ring of powerful cilia on 

 an ectodermal thickening of its wall. A pair of short antero-pos- 

 teriorly flattened lobes at the right and left sides of the body is the 

 rudiment of the aliform notopodia. Its position directly back of 

 the thickened ciliary ring sviggests that the ciliated groove of the 

 notopodia is a vestige of the dorsal half of this ciliary ring, and that 

 the notopodia are themselves formed by an excessive growth dorsal- 

 wards of the rie-ht and left sides of the rings. On its ventral side 



