SURVEY OF INVERTEBRATES 65 



this habitat offers for anaerobic worms. ZoBell and 

 Feltham (1942) found several undetermined species at 

 depths exceeding 40 cm. in a marine mudflat where com- 

 pletely anaerobic conditions prevailed. The observa- 

 tions of Moore (1931) are also very significant in this 

 connection. He investigated the bottom fauna of the 

 mud in the Clyde Sea area (Scotland), in a region where 

 the interstitial water was completely free of oxygen at 

 the very surface. He found large numbers of unidentified 

 nemalpodes in the upper 4 cm. and a few down to a depth 

 of 7 cm. Unspecified polychaetes, most of them imma- 

 ture forms, were encountered only in the uppermost cen- 

 timeter, and only a few went down as far as 5 cm. Moore 

 (1931) thinks it possible that the nematodes in question 

 might live permanently without oxygen. He exposed 

 these worms to an experimental anaerobic medium for a 

 period of 35 days after which they still appeared normal 

 and active. 



Another question of interest is whether worms living on 

 the sea shore are normally exposed to anaerobic condi- 

 tions at low tide. Many of these worms live in tubes and 

 have but little chance to renew rapidly the water that 

 fills these tubes, water on which they depend for their oxy- 

 gen supply. If any is renewed, the replacement will not 

 be with water rich in oxygen but with the oxygen-poor 

 water that permeates the ground. This does not neces- 

 sarily imply that the worms must live in a predominantly 

 anaerobic manner. It is possible that they stir up the 

 water present in the tubes, causing it to circulate and thus 

 giving it a chance to absorb oxygen directly from the at- 

 mosphere. This seems to happen in Areuicola, but wheth- 

 er it occurs in worms like Scoloplos, Hcferomastus or 

 Nephthys has not yet been definitely decided (Tham- 

 drup, 1935). 



The case of Arenicola has been studied thoroughly by 

 Borden (1931). She found that the haemoglobin-con-, 

 taining blood of this animal plays an important role in 



