1901.] AND TOUNCI OF A POLTCHiETE WORM. 719 



had been hatched about 150 hours. They measured about -75 mm. 

 iu length, and were '16 mm. in breadth at the broadest part — the 

 first pair of parapodia. There were four seta-bearing segments, 

 each with a pair of parapodia, the hotter growing progressively 

 smaller from before backwards. The first parapodium bears two 

 simple and two compound setsB, the rest have only compound. Of 

 these there are two kinds — those with a triangular end-piece like 

 the first-formed ones, and others with a narrower sabre-like appen- 

 dage. With the two setaless segments in front and the terminal 

 segment (bearing traces of the fifth seta-sac) there is a total of 

 seven, exclusive of the head. Each is separated from its neighbours 

 by a well-marked annular depression, and the parapodia, which 

 are still nniramous, stand up sharply above the general surface of 

 the body. At the hind end the anal processes or cirri are longer 

 than the terminal segment, taper to a point, and are directed 

 outwards. In front of them a pair of small knobs arise from the 

 hinder angles of the terminal segment, apparently the rudiment 

 of a second pair of cirri. 



In the interior of the body there is now a distinct body- cavity 

 surrounding the gut, into which project the seta-sacs provided 

 with well-developed muscles. The gut consists of a pharynx, a 

 dilated stomach, a narrower intestine, and a ciliated rectum. 

 The jaws are well developed and amount to seven pieces at least. 

 Of the several parts of this apparatus in an adult Eunicid the 

 forceps alone appear to be wanting. 



It is interesting to compare the larval history just described 

 with those of the other Eunicids in which the same processes have 

 been followed. These fall into three groups ^ : — 



i. The free-swimming larva?, all of unknown species, described 

 by Miiller (6), Krohn and Schneider (6), Claparede and 

 Metschnikoff (1), and Haecker (3). 



ii. The larvae of Lumhriconereis sp. and Diopalra magna, 

 described by Eewkes (2) and Wilson (9, 10) respectively. 

 These pass through the whole of their earlier stages in the 

 spawn-jelly, and leave as young worms with several pairs 

 of parapodia. There is no free-swimming stage. 



iii. The embryos of Marpliysa sanguinea described by Koch (4)", 

 which pass through their earlier stages in the body-cavity 

 of the mother and are born as young worms. 



The larvae of the present species of Marphgsa are clearly allied 

 with the first of these groups rather than with either of the others. 

 This is shown by the form of the body, the arrangement of the 

 ciliation and its successive phases, the presence of two eye-spots 

 and only two, and the early hatching-stage. Also the course of 

 development differs in no important feature in the two cases, so 

 far as they are known. But it would appear that the same cause, 



1 Ophryotroclia would form a fourth group, independent of the otliers, polj-- 

 trochal and free-swimming. 



- For the later stages, see Webster (8)- 



^ 47* 



