ANATOMY AND CLASSIFICATION OF THE ARENICOLID^. 559 



Fig. 7.— The gill of A. ecaudata. 



Tig. 7 a.— Tlie third left gill, to show the plan of branching from the 

 base. X 10. 



Fig. 7 b.— The terminal branches of one of the gill plumes. X 10. 

 The gill of A. Grubii closely agrees with this. 



PLATE 23. 



Fig. 8. — A. marina. Neuropodial chsetse from the post-larval specimen 

 (3'9 mm. long) shown in Fig. 34?. Note the rostrum (RosL), the teeth [T.), 

 and the process (Proc). The last is more highly developed in, and very 

 characteristic of Maldanidae. X 1000. 



Fig. 9. — A. marina. The ventral portion of the neuropodium of a large 

 Laminarian specimen, showing the stages in development of the chsetse. The 

 line marked Nm. is the outline of the neuropodium. The clipctse are devoid of 

 teeth, but show a small blunt process {Proc). X 85. 



Fig. 10. — A. marina. A neuropodial chasta from a littoral specimen 

 100 mm. long. In worms of this size the chsetse bear two or three small 

 teeth, and a very minute blunt process. X 150. 



Fig. 11. — A. marina. A neuropodial chseta from a small specimen 

 17 mm. long. The teeth are well marked, x 500. 



On comparing the four preceding figures there is seen to be, following the 

 growth of the worm, an increase in the size of the chsetse, a decrease in the 

 size of the teeth of the chsela?, and also a gradual change in the incli- 

 nation of tiie rostrum to the shaft, the angle increasing with the size of the 

 specimen. 



Fig. 12. — A. marina. Notopodial setae from the post-larval specimen 

 (3"9 mm. long) shown in Fig. 34. Each notopodium bears about two to five 

 ordinary capillary chsetse (Fig. 12 a), and one similar to those shown in 

 Fig. 12 b. 



Fig. 12 a. — Capillary seta showing the barbs or processes upon its distal 

 portion, x 500. 



Fig. 12 b. — Notopodial setse bearing a lamina along a portion of their 

 length. X 1000. 



Fig. 13. — A. cristata. 



Fig. 13 a. — Represents a notopodial seta from a specimen 47'5 mm. long 

 from Jamaica, to show the barbs or processes upon its distal portion. X 93 



Fig. 13 b. — A portion of the same seta from the region marked +, more 

 highly magnified, x 1000. 



Fig. 14. — A. cristata. The tip of a notopodial seta from the large 

 specimen shown in Fig. 30. Note the very numerous barbs or processes. 

 X 500. 



