IQ2I.] Fauna of the Chilka Lake : Polychaeta. 587 



In the 63rd foot the dorsal cirrus is 2-J times as long as the dorsal ligule. 

 The dorsal division is relatively still larger and more prominent than the ventral 

 division. The upper group of the ventral division consists only of a single thick 

 falcate heterogomph, the spinose homogomphs having disappeared. 



There are four types of setae present in this species, in addition to the 

 modified setae of the Heteronereid phase. In the dorsal division only homogomphs 

 with long tapering spinose tips occur (fig. 8n) . In the ventral division, the anterior setae } 

 above and below the spine, are falcate heterogomphs (fig. 8p). They have moderately 

 long terminal pieces, smooth at the tip, spinose below. The posterior setae consist 

 of an upper group of spinose homogomphs, similar to those in the dorsal division, 

 and a lower group of spinose heterogomphs. Between the 20th and 30th feet two or 

 three setae appear in the upper anterior group of falcate heterogomphs of the 

 ventral division, which have shafts rather thicker than those of the other setae. 

 In the subsequent feet these setae increase in thickness, but diminish in number, and 

 in the last few feet, as already stated, the upper ventral group is represented only 

 by a single falcate seta with a shaft three times as thick as that of the normal type 

 of seta. The terminal piece is relatively shorter, with only a few strong spines on the 

 edge (fig. 8q). The shafts of the falcate setae of the lower group also increase in 

 thickness in the posterior feet, but not to the same extent. 



There is considerable variation in this species. In some individuals the tentacu- 

 lar cirri and dorsal cirri are much longer than usual (fig. 8b) . 



The terminal pieces of the very thick ventral falcate setae have sometimes only 

 three or four spines, and rounded tips, as in fig. 8q, but in other specimens they may 

 have ten or twelve spines, and pointed tips. This character doubtless depends on 

 the amount of wear they have undergone. The eyes vary considerably in size, as do 

 the paragnaths, and the intensity of the epidermal pigment. Some or all of these 

 characters may be associated with approaching change to the Heteronereid condition. 



Three specimens of this species were taken which had, in varying degrees, assum- 

 ed the Heteronereid condition. The more advanced of the two female specimens was 

 selected for examination. It is 40 mm. long, with 63 setigerous segments. The 

 colour of the dorsum is much deeper than that of the immature individuals, and the 

 eyes are much larger, but not connate. The paragnaths on the basal segment of the 

 proboscis are larger than usual. The anterior 18 pairs of feet show no change. In 

 the 19th foot the ventral cirrus shows indications of a small ventral lobe near the 

 base. The 20th foot has a few of the characteristic swimming setae in both divisions 

 of the foot, and the basal lobe of the central cirrus is well developed. The setigerous 

 lobes and their fillets are enlarged. 



In the 25th foot (fig. 8j) the dorsal cirrus remains unchanged. The ventral cir- 

 rus has a large ventral and a small dorsal wing near the base. The three ligules are 

 elongate and pointed. The two lobes of the ventral setigerous division are enlarged 

 and flattened, and the posterior one has two flat wings. The setae are mostly of the 

 natatory type, but a few of the old setae remain. In the 30th foot the flattening of 

 the various lobes is more obvious. In the 40th foot (fig. 8k) the dorsal cirrus has a 



