SEA-FISHERIES LABORATORY. 267 



more rapid. One or two eyes of orange-red colour were 

 also present on the anterior portion of the larva. During 

 the third day the animal elongated and contracted at in- 

 tervals, and evidently both longitudinal and circular 

 muscle fibres were present. At the end of the third day 

 the telotroch* larva worked its way out of the vitelline 

 membrane through a thin area which had previouslj^ made 

 its appearance (fig. 75). 



When hatched the larva was about "25 mm. long-. It 

 either crawled on the bottom of the dish or swam actively 

 by means of its cilia. Between the two bands of cilia 

 there appeared on the ventral surface a broad longitudinal 

 band of short cilia. Soon after hatching a small spade- 

 shaped seta (7^t long) was observed in one specimen. It 

 could be protruded and retracted (fig. 76). The larvae 

 grew very slowly in the laboratory and it was not until 

 more than four days after hatching that the setae of. the 

 following segment appeared. In the meantime the 

 spatulate setse of the first segment had beeu reinforced by 

 the addition of a seta with a long, drawn-out tip, and a 

 little ventral to this the first crotchet appeared. Two days 

 later the alimentary canal seemed to be complete from 

 mouth to anus, its central part was rather distended with 

 yolk. The ccelom was quite obvious post-orally, and the 

 ventral body wall was thickened, due to the formation 

 there of the ventral nerve tract. The two belts of cilia 

 and the longitudinal ventral band gradually decreased in 

 size from this point onwards. Two days later another 

 segment acquired its setae. Both the chaetigerous seg- 

 ments in front of this had on each side two setae and a 

 crotchet, the third segment bore only the newly formed 

 spatulate seta. The larvae crawled about the bottom of 



* The term applied to Polycheete larvae in which the cilia are 

 arranged in two bands forming a preoral and a peri-anal ring. 



