SEA-FISHERIES LABORATORY. 313 



Fig. 14. A portion (0"2 mm. from the tip) of a seta 

 (2" 5 mm. long) from a littoral specimen 125 mm. long. 

 On the left the lamina, with its dentate margin, is shown, 

 x 800. 



Fig. 15. Two crotchets from nenropodia of a post- 

 larval specimen 5*1 mm. long. The teeth on the sides of 

 the rostrum are indicated. The dotted line indicates the 

 level of the epidermis. x 1,000. 



Fig. 16. Neuropodial crotchet from a young littoral 

 specimen 17 mm. long. x 500. 



Fig. 17. Neuropodial crotchet from a littoral speci- 

 men 125 mm. long. x 150. 



Fig. 18. Ventral portion of neuropodium of Lami- 

 narian specimen 250 mm. long. On the left (which is 

 ventral) the various stages of formation of the crotchets 

 are seen. The crotchet on the right is fully formed. 

 Nm shows outline of the neuropodial sac. x 75. 



On comparing the four preceding figures there is seen 

 to be, as the worm grows, an increase in the length of the 

 crotchets, a decrease in the size of the teeth behind the 

 rostrum, and also a gradual change in the inclination of 

 the rostrum to the shaft, the angle increasing with the 

 size of the specimen. 



Fig. 19. Hight aspect of tenth and part of ninth 

 ehaetigerous segments of Laminarian specimen (190 mm. 

 long). The fourth gill has eleven main stems united at 

 their bases by a membrane. Five of these, and many lateral 

 branches, have been cut away to show the remainder. The 

 ventral stem alone, in which the lateral branches have the 

 simplest form, is shown entire. Lateral branches some- 

 what simplified. Fig. 21 shows one in detail. The 

 third gill has been almost entirely cut away. The 

 capillary setse are seen projecting beyond the lips of the 

 notopodial setal sac. Each neuropodium resembles a 



