136 A ren icolidae 



the worms contract, but soon extend in well aerated water to nearly 

 twice their reduced length. 



COLOUR. The colour of this species varies from dark brown or 

 black, with greenish metallic sheen, to light reddish brown. Most 

 of the British examples seen by the writer are of a yellowish red or 

 brownish red tone, and with a purple anterior region, as shown in 

 PL II, Fig. 7, but about one-third of the specimens collected are 

 much darker, being coloured almost exactly like the example of 

 A. branchialis figured on the same plate (Fig. 5). 



VARIATIONS IN THE ORGANS. The most striking variation is in 

 regard to the number of segments. Adult specimens of this species 

 seldom exhibit as many segments as they possessed at the end of the 

 post-larval stage, but occasionally an unabbreviated example is met 

 with, in which case the number of segments is about sixty to 

 sixty-four. There are about forty-five to fifty segments in average 

 specimens. 



The number of gills depends, of course, chiefly on the number of 

 chaetiferous segments, but even in unabbreviated specimens there 

 may be some reduction in the gill-series anteriorly, or posteriorly, or 

 at both ends. In about twenty per cent, of the specimens examined 

 the normal first gill (that is, that on the sixteenth segment) was 

 found wanting on both sides, and in a further twenty per cent, on 

 one side. The last segment is not uncommonly abranchiate, and 

 the writer has seen specimens with two, three, four, six and nine 

 posterior abranchiate segments respectively. 



Prof. Fauvel states that in his examples of A. ccaudata the 

 number of nephridia is "12 paires, parfois 13," the last nephridium 

 usually opening on the sixteenth segment, but all the British 

 specimens examined by the writer possess thirteen pairs, and there 

 was no sign of reduction of the last pair. 



PERIOD OF MATURITY, DEVELOPMENT. A. ccaudata was found to 

 be mature, in the neighbourhood of Port Erin, during April, 1897, 

 for the nephridial vesicles of specimens then dissected were greatly 

 dilated with ova ready to escape. Ripe examples were obtained from 

 Plymouth at the end of August, 1910, and from these Figs. 52 

 and 53, PI. XV, were drawn. Whether there is for this species 

 in Britain one continuous period of maturity, extending from the 

 beginning of April to September, or there are two periods, separated 

 by a non-breeding interval, the writer has not had the opportunity of 



