90 



Mr. E. Ray Lankester on the Organization 



Table II. — Supplementary List of peculiar Arenaceous Forms. 

 See fiffs. 1—4 and 7. 



XI. — Outline of some Observations on the Organization of 

 Oligochcetous Annelids. By E. Ray Lankester, B.A. Oxon. 



For some time past I have, as opportunity offered , exa- 

 mined the structure of the freshwater and terricolous Annelids. 

 I have already published an account of the larval form of 

 Chatogaster (Trans. Linn. Soc. 1868), and of its sexual foi-m 

 (Quart. Journ. Microscopical Science, 1869), to which I have 

 now something to add ; I have also briefly described the re- 

 markable genital set^e which characterize Nais equally with 

 Choitogaster (Ann. and Mag. Nat. Hist. 1869), and have 

 shown that the Naididse as a group present in their develop- 

 ment two very distinct forms — the one larval, reproducing 

 by fission, the other sexual, of a limited number of segments, 

 provided with additional segments interposed between seg- 

 ments present in the larva, arising by new growth, bearing 

 peculiar setse and the generative organs — the seta of the whole 

 worm differing also to some extent in the adult and larval 

 forms. 



The mud-banks of the Thames about and below London 

 swarm with countless masses of red worms belonging to the 

 Sa?nuridje; and these, besides others from ponds at Hampstead, 

 have furnished me with abundant material. I propose to give 

 a short statement of some new facts, which I hope to illustrate 

 with detailed drawings hereafter. The immense profusion of 

 the worms in the Thames mud, of Avliich they are the almost 

 solitary occupants of high organization, is sui-prising. They 

 appear to exist under the most favourable conditions as re- 



