238 J. H. ASHWORTH.- 



1. Introduction. 



My attention was drawn to our scanty knowledge of 

 Scalibregma when discussing the affinities of Arenicola 

 with other Polychtetes (1900/ p. 544). It was found impos- 

 sible to make any definite statement regarding the affinities 

 of these two genera, owing to the small amount of informa- 

 tion available regarding the structure of Scalibregma. 

 This Polych^te has received little attention from zoologists, 

 perhaps on account of its comparative rarity and the some- 

 Avhat small size of the majority of specimens in museum 

 collections. Most of the references to this animal in zoolo- 

 gical literature are mere records of its capture. There are 

 only three or four memoirs which refer, quite briefly, to some 

 details of its structure, and only one, by Danielssen (1859, 

 p. 69), which contains a connected account of its internal 

 anatomy. This memoir contains no mention of the nephridia, 

 although the accompanying figures show structures which 

 are obviously nephridia, but which Danielssen considered to 

 be ovaries. He also stated that Scalibregma is hermaph- 

 rodite, and that its nerve-cord is provided with typical 

 ganglionic swellings. Subsequent authors do not throw light 

 on any of these matters. In these points there was such 

 marked difference between Scalibregma and Arenicola, 

 which in other respects seemed to have much in common, 

 that I was anxious to reinvestigate the anatomy of the 

 former as soon as specimens were available, chiefly with the 

 intention of comparing the nephridia, gonads, and nerve-cord 

 of these two genera. The material placed at my disposal has 

 enabled me to study the anatomy and histology of this 

 northern Annelid, and to determine some interesting points 

 connected with most of the systems of organs. 



I am grateful to the authorities of the United States 

 National Museum in Washington for the loan of a number 

 of specimens collected on the east coast of America, and to 



' The dates in parentheses form references to the hterature quoted at the 

 end of this paper. 



