HABITS AND STRUCTURE OF ARENIOOLA MARINA. 33 



and contain mature ova or spermatozoa, so that upon irritation 

 a simultaneous discharge through all these 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 ovipositiou 

 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 Phyllodoce 

 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 tiiat the 

 number of both tliese 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. Claparedii have five pairs of 

 nephridia, and apparently the same number of gonads, whereas 

 A. ecaudata has no less than thirteen pairs of ne])hridia, 

 twelve of which bear large and complicated gonads of a size 

 and complexity which is scarcely equalled by any other Poly- 

 chset. What relations exist between A. marina 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. 



VOL. 41, PART 1. — NEW SEB. 



