ON CH^TOBRANOHUS. 89 



worm which he discovered in the Philippine Islands is un- 

 doubtedly either the same or a closely allied species. 



It is impossible^ in dealing with a single species such as 

 this, to define the specific characters; the absence of eye-spots, 

 the character of the setae, the length of the branchial processes, 

 the nature of the pigmentation, will probably serve, among 

 other characters, to mark the species. 



DESCRIPTION OP PLATE XII, 



Illustrating Professor A. G. Bourne's paper "On Cheeto- 

 branchus Semperi.''^ 



Fig. 1. — Lateral view of CliEetobrauchus ; the branchial processes and 

 dorsal and ventral setae of one side only are drawn, pr. Prostomium. m. 

 Mouth, an. Anus. 



Fig, 2. — A single branchial process, s. Dorsal setae, a. Afferent blood- 

 vessel, e. Efferent blood-vessel. 



Fig. 3. — A portion of the dorsal blood-vessel. /. A pair of lateral vessels. 



Fig. 4. — A portion of the ventral blood-vessel. /. A pair of lateral vessels. 



Fig. 5. — A capillary seta from a dorsal seta bundle. 



Fig. 6. — A seta from a dorsal seta bundle, with a sickle-shaped free 

 extremity. 



Fig. 7. — a. A seta from a ventral seta bundle in the posterior region of 

 the body, b. The free extremity of a similar seta from the anterior region of 

 the body. 



Fig. 8. — A coelomic corpuscle. 



Fig. 9. — Dorsal view of Chsetobranchus. Natural size. 



Fig. 10. — A "budding" individual of Chsetobranchus. About twice 

 the natural size. 



