90 



Mr. E. Ray Laukester on the Organization 



Table II. — Sujjpleinentary List of peculiar Arenaceous Forms. 



See fiofs. 1-4 and 7. 



XI. — Outline of some Ohservations on the Organization of 

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



For some time past I Iiave, as o])portunity offered, exa- 

 mined the striictm'e of the freshwater and terricolous Annelids. 

 I have ah*eady published an accomit of the larval form of 

 Cha'togaster (Trans. Linn. Soc. 1868), and of its sexual form 

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

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

 markable genital sette which characterize Nais equally Avith 

 Cha'togaster (Ann. and Mag. Nat. Hist. 1869), and have 

 shown that the Naididai 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 setae and the generative organs — the setae 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 

 Saenuridse; 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 which they are the almost 

 solitary occupants of high organization, is surprising. They 

 appear to exist under the most favourable conditions as re- 



