SEA-FISHERIES LABORATORY. 211 



Typical specimens of A. marina are found in the 

 littoral zone. Their burrows are usually U-shaped (see 

 p. 30). One end of the burrow is marked by a casting; 

 and the other by a funnel-shaped hole through which the 

 head was probably withdrawn, and through which it may 

 be again protruded when the burrow is covered by the rise 

 of the tide. The worm is almost invariably found head 

 downwards in such a position that the tail and posterior 

 part of the body lie in the limb of the burrow connected 

 with the casting, while the head and anterior part of the 

 body lie either in this or in the horizontal limb of the TJ. 

 The worms average about seven to nine inches in length," 

 and their gills, which are best developed in old, deeply- 

 pigmented specimens, are composed of nine to eleven 

 stems each provided with three to five pairs of short 

 lateral branches (fig. 22). These littoral forms breed in 

 the spring, usually from the end of February onwards for 

 about a month but specimens containing ripe ova may be 

 occasionally met with up to the end of April,t and on the 

 Lancashire coast even later. The smallest specimens 

 found in the sand are 17 mm. in length (see p. 269), 

 possibly smaller ones are present but have escaped obser- 

 vation. Young specimens are pinkish in. colour, due to 

 the fact that numerous blood-vessels are seen through the 

 translucent body-wall, and their gills are usually bright 



* The largest specimens of the littoral variety I have seen, are 

 several found near Musselburgh, on the Firth of Forth, measuring 

 360 mm. (about 14J inches) in length. 



f I am inclined to believe that, in some localities at any rate, 

 Arenicola marina also breeds about August or September. Large 

 specimens weie taken near Musselburgh in July, 1903, which contained 

 great numbers of ova and sperms in an almost ripe condition. In 

 other full-grown specimens from the same area, taken near the end of 

 October, not a single large egg or mass of spermatids was to be found. 

 Among the specimens examined on both occasions were both littoral 

 and Laminarian forms. In others, taken early in January, 1904, 

 genital products are small and scarce in the coelomic fluid. 

 A month later, in males, spermatogonia and spermatids, and in 

 females young ova (-06 mm. in diam.) are present in quantity. 



