572 Memoirs of the Indian Museum. [Voe. V, 



Sexual Maturity. 



In an environment like that of the Chilka Lake it may well be that some species 

 are able to live throughout the later larval and adult periods of their life, without 

 being able to reproduce there (Annandale and Kemp, 1916, p. 337). Free-swimming 

 adults and larvae, or eggs, may be periodically carried into the lake by favourable 

 winds, currents and tides, to places which are suitable for their further growth. 

 This is much more probable in the case of those species which live in the Outer 

 Channel than in those which occupy the main area of the lake. Such a sterile migra- 

 tion is much more probable in the case of mobile animals like the fishes and 

 Crustacea than in such a relatively sedentary group as the Polychaeta. Of the 20 

 species found in the lake, 8 contained genital products more or less mature, the species 

 Nereis chilkaënsis being represented by the Heteronereis in all stages of maturity. 

 A number of quite small and immature individuals of several species were also collec- 

 ted. Probably the majority of the Polychaeta, if not all, are permanent residents. 

 The subject is worthy of further investigation. 



Habitat of the Chieka Lake Poeychaeta. 



Five types of habitat may be provisionally distinguished. Information on this 

 subject is very defective, and the scheme may be greatly modified by further obser- 

 vations. 



Species found mainly or wholly on a muddy bottom. 



Ancistrosyllis constricta. Lumbriconereis simplex. 



Nephthys polybranchia. Glycinde oligodon. 



Nephthys oligobranchia. Myriochele picta. 



Diopatra variabilis. Euclymene annandalei. 



Marphysa gravelyi. Laonome indica. 



Species found mainly or wholly on a sandy bottom. 



Tylonereis fauveli. Lumbriconereis polydesma (?) . 



N er eis chilkaënsis (?) . Scoloplos marsupialis. 



Nereis reducta. Sternaspis costata. 



In the case of the two species queried, the distribution in the lake would lead 

 one to expect a muddy habitat, though the labels attached indicate sand. 



Species found on the oyster bed at Manikpatna in the Outer Channel. 



Ancistrosyllis constricta (on one occasion). 



Perinereis marjorii. Polydora hornelli. 



The last named only is a true shell-borer ; the two former species probably only 

 take shelter amongst the oysters. 



Species living in sponges (Spongilla and Laxosuberites). 



Nereis chilkaënsis. Fabricia spongicola. 



Species living amongst weeds. 



Nereis chilkaënsis. Fabricia spongicola. 



