THE HABITS AND STRUCTURE OF ARENICOLA MARINA. 115 



apertures may occur. In one worm only eight inches in length the 

 bladder of the nephridium was swollen with ova so as to measure 

 14 mm. in length and 6 mm. in width. During the discharge of ova 

 from the female the eggs are caught by the slimy mucus covering of 

 the body, and, owing to the movements of the animal, collect in strings 

 round the body. We have not observed the formation of gelatinous 

 capsules in which the eggs may be laid, since we have not worked at 

 the oviposition of this species, about which nothing is at present 

 known. At certain times of the year, chiefly in the spring, the nets 

 used by shrimpers on the sandy coast near Lytham are almost choked 

 by the balls of eggs, each moored by two " cables " to the sand. 

 Whether these eggs belong to Arenicola remains to be seen, but their 

 form differs from that of Phyllocloce found so commonly in early spring. 

 It has generally been assumed that the number of nephridia and 

 gonads occurring in Arenicola marina is typical or fairly typical of the 

 genus, and it is usually stated that the number of both these organs 

 is a small one (five or six). An investigation of several other species 

 of Arenicola, the results of which .we hope shortly to publish in full, 

 have shown that A. Grubii and A. CUvparedii have five pairs of neph- 

 ridia, and apparently the same number of gonads, whereas A. ecaudata 

 has no less than thirteen pairs of nephridia, twelve of which bear large 

 and complicated gonads of a size and complexity which is scarcely 

 equalled by any other Polychset. What relations exist between A. 

 maricea and the other species of the genus cannot be discussed here, 

 but it may be stated generally that the genus exhibits greater variety 

 in the development of several systems of organs than has been hitherto 

 suspected, and that it is no longer possible to exemplify the characters 

 of Arenicola as a genus by using their particular grade of development 

 in A. marina as a type. 



12. General Summary. 



The following is a recapitulation of the new points which we have 

 found in Arenicola marina. 



1. On the Lancashire coast, and probably elsewhere, two well-marked 

 varieties of Arenicola marina occur, differing, as the following table 

 shows, in general appearance, in their habits, in the structure of their 

 gills, and periods of maturity. 



