1901.] AND YOU NO OF A POLTCH/ETE WORM. 719 



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

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

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



each with a pair of parapodia, the latter growing progressively 

 smaller from before backwards. The first parapodium bears two 

 simple and two compound seta\ 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 setalesa 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 

 arc still uuiramous, 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 part* of this apparatus iu 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 larvae, all of unknown species, described 

 by Midler (6), Krohn and Schneider (5), Claparede and 

 Metschnikoff (1 '), and Haecker (3). 



ii. The larva- of Lumbriconereis sp. and Diopalra magna, 

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

 These pass through the whole of their earlier stages in the 

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

 of parapodia. There is no free-swimming stage. 



iii. The embryos of Marphysa sanguinea described by Koch (4)-, 

 which pass through their earlier stages in the body-cavity 

 of tin 1 mother and are born as young worms. 



The larva of the present species of Biarphysa arc clearlj allied 

 with the lit'-! 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 it- successive phases, the presence of two eye-spots 

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

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

 far as they are known. Bui it would appear thai the same cause, 



1 Ophryotrocha would forma fourth group, independent oftl then, poly- 



troche! and free-swimming. 



the later itagee, mi Webster (8> 



17- 



