434 DE. H. C. SOEBT ON SOME SPECIES OE NEREIS 



EXPLANATION OF PLATE 43. 



Fig. 1. Colony (without attachment) (nat. size), showing the unilateral method 

 of branching ; also a part of the axis devoid of ecEnenchyma, showing 

 the ridges and furrows ; also the internodal origin of the branches. 



2. Typical colony (nat. size), showing the palmate terminations of the twigs. 



3. Tip of a branch ( X 10) with one half cut away, showing (i) the excessive 



thickness of the coenenchyma ; (ii) the longitudinal nutritive canals ; 

 (iii) the retracted polyps sunk in cavities in the coenenchyma ; (iv) the 

 enormous embryos in situ ; (v) the thick muscular bands. 



4. Part of the surface of the coenenchyma enlarged (Xl4), to show the 



polyps in different stages of retraction, with the small mound-like 

 elevations. 



Notes on some Species of Nereis in the District of the 

 Thames Estuary. By H. C. Sorbt, LL.D., F.E.S., F.L.S. 



[Eead 1st March, 1906.] 



PoE more than 20 years I spent four or five months each summer 

 (May to September) on board my yacht ' Glimpse ' in various 

 parts of Kent, Essex, and Suffolk, devoting myself much to the 

 study of the marine animals. During this time I was able to 

 observe a number of interesting remarkable facts connected with 

 the Seteronereis form of two species oi Nereis, which occur rarely. 



Except in a few rare cases, when properly mounted in balsam, 

 the natural colour is to a great extent preserved, and it is quite 

 easy to see the form and colour of the jaws, even when completely 

 retracted, and the form and colour of the prickles about the head, 

 and of the eyes, as seen by transmitted light, and the ova, when 

 present, which is not the case when specimens are preserved in 

 alcohol or formalin. 



The species found by me in the district of the Thames estuary 

 are as follows : — 



1. Nereis diversicolor. Miiller. — Often very common in the 

 mud of the estuaries left dry at low water, but rare in 

 some of them. 



2- N. Dwnerilii, Audouin & Milne - Edwards. — Living in 

 tubes formed amongst the marine plants. It must be 

 numerous in some localities, but often lost when the plants 

 are dredged up. 



3. N. longissima, Johnston. — Very rarely found in the mud, 

 but must be fairly common in some places. 



