SEA-FISHERIES LABORATORY. '285 



animal are so arranged as to leave the stomach consider- 

 able freedom of movement. 



The Arenicolidse agree with the Scalibregmidge in the 

 points named above, in the general shape of the body, the 

 snb-division of the segments into annuli, the sculpturing 

 of the skin, the small lobed prostomium, and the presence 

 (in Scalibregma and Eumenia) of gills of a similar type. 

 The brain and non-ganglionated nerve cord of the caudate 

 Ar'enicolidse is similar to that of the Scalibregmidae. 

 There are also points of difference between these two 

 families which are of considerable importance. In the 

 Scalibregmidse the two rami of the parapodia are practi- 

 cally identical, but they are very different in the Areni- 

 colidse. In the latter the neuropodium bears crotchets 

 only, and the notopodium bears capillary setae, while in 

 the Scalibregmidse both rami bear two kinds of setae, 

 capillary and furcate, the latter being characteristic of the 

 family. In some of the Scalibregmidse the parapodia 

 form laminate appendages bearing dorsal and ventral 

 cirri, which are not found in Arenicola (cirri are occasion- 

 ally seen in the posterior region of American specimens of 

 A. cristata). The gills of Scalibregma and Eumenia are 

 confined to the first five segments, on which they never 

 occur in Arenicola. The heart in the Scalibregmidee is 

 a median structure, while in Arenicola there is a pair of 

 hearts. The nephridia of the Scalibregmidse are minute, 

 but numerous, the simple microscopic funnel leading into 

 a slender U-shaped tube; the nephridia of Arenicola are 

 few in number and wide and sac-like, each having a large 

 funnel fringed with ciliated vascular processes. Several 

 of the Scalibregmidae bear complex segmental lateral 

 sense-organs which are not found in Arenicola. 



The Arenicolidse have a few characters in common 

 with the Opheliida?, but the accounts of the latter family 



