SEA-FISHERIES LABORATORY. 269 



in which all the gills are present, and it would therefore 

 appear that most specimens take to a littoral habit rather 

 earlier than this one. In point of length it is not, how- 

 ever, a large specimen, being only 3"9 mm. long. In life 

 it would certainly be longer; this measurement is taken 

 from the mounted specimen, which was unfortunately 

 preserved in a somewhat contracted condition. The 

 longest post-larval stage I have seen measures 6 - 5 mm. 

 from anterior to posterior ends, and this one has no gills. 

 Evidently, therefore, the time of appearance of these 

 organs varies in different specimens. Perhaps the two 

 specimens under consideration belong to the two different 

 varieties of ^4. marina, but there are no means of establish- 

 ing this point in the larger specimen; the smaller almost 

 certainly belongs to the littoral variety. 



Nothing is known concerning the duration of 

 the pelagic life of these post-larval stages, but it is 

 apparently at any rate some days, judging from the 

 varying sizes of the specimens captured within a few days 

 of each other. For example, in a series of eight speci- 

 mens taken near Plymouth during the last days of March 

 and early days of April, 1901, there are specimens varying 

 from 35 to 6"5 mm. in length. Again, the varying sizes 

 of these specimens, and the length of the period during 

 which they may be taken in the tow-nets, show that the 

 spawning period of A. marina may occasionally extend 

 over two or three months, e.g., post-larval stages have 

 been taken as early as March 8th, and as late as May 29th. 

 The latter date is, however, exceptionally late ; most 

 specimens are taken either in March or in the early days 

 of April. The smallest worms I have found in the sand 

 were taken near the end of June, and are IT mm. long. 

 They possess thirteen pairs of well-branched gills, the 

 prostomium has assumed the adult form and relations, 



