PLATE XVIII. 



Fig, 



1. Dorsal view of the head of Lineus marinus after long confinement. The blanching of the 



cutaneous tissues renders the eyes conspicuous. Magnified under a lens. 



2. Ventral view of the same specimen exhibiting the mouth (w). Similarly magnified. 



3. Profile of the same head, showing a cephalic fissure with its reddish coloration posteriorly. 



4. Transverse section of the body- wall of Lineus gesserensis. X 350 diam. 



5. Transverse section of the body-wall of Lineus marinus at a somewhat narrow portion. 



d, external cuticular layer ; d", pigmentary layer divided into two strata by a definite black 

 band (2) ; 3, curious translucent stratum cut into regular spaces. Other letters as usual. 

 X £10 diam. 



6. Longitudinal section of the same tissues. 4, 4, sections of the transverse connecting trunks 



between the lateral and dorsal vessels ; 5, granular stroma within the inner longitudinal 

 muscular coat, supporting the former and various other tissues. X 90 diam. 



7. Transverse section just behind the tip of the snout of L. gesserensis. The grouping of the 



pigment (3) readily enables the observer to distinguish the dorsal from the ventral surface ; 

 2, powerful series of fibres arching over the channel for the extrusion of the proboscis, and 

 radiating into the surrounding stroma (k), X 55 diam. 



8. Transverse section somewhat behind the preceding, and through the anterior part of the 



cephalic fissures. The channel for the proboscis has become more central in position. 

 The superior pigmentary belt (3) is somewhat narrower, and an inferior (4) has now 

 appeared. The central channel has a layer of longitudinal muscular fibres internally, and 

 a powerful series of oblique and circular fibres (2, 2) form a very efficient exterior invest- 

 ment. X 55 diam. 



9. Transverse section of the cephalic ganglia of a smaller specimen than the preceding. 



X 55 diam. 



10. Horizontal section of the snout of the same species through the ganglia, exhibiting the 



relations of the latter and the reticulations of the cutaneous tissues in front of them. 

 X 90 diam. 



11. Transverse section of a specimen of L. gesserensis (after spawning) a little in front of the tip 



of the tail. X 90 diam. 



12. Elements from the glandular papillae of the proboscis of the same species, after their escape 



into the water. X 700 cliam. 



13. Elements from the proboscis of Micrara faseiolata. Similarly magnified. 



14. Portion of the inner surface of the proboscis of L. gesserensis, showing the glandular papillae. 



Slightly compressed. X 700 diam. 



15. Snout of Cephalothrix linearis with the proboscis slightly everted, so as to exhibit the 



acicular papillae. X 350 diam. 



16. Fragment of the wall of the proper digestive chamber of L gesserensis. The cilia mark 



the inner surface. X 350 diam. 



17. Parasitic ciliated animal from the tissues of the same species. The letters a, b, c, and d 



correspond with the groups of segments described in the text. X 350 diam. 



18. The foregoing parasite at an earlier stage of development. X 350 diam. 



19. The last-mentioned specimen subjected to slight pressure, so as to exhibit the segments. 



X 350 diam. 



