THE ANATOMY. SENSE ORGANS 13 



arise from the cerebral ganglia and end in these processes ; however, it is common 

 among the Oligochaeta for the epidermis of the prostomium to be modified to the extent 

 that it has no gland-cells and is formed of deeper cells than is the epidermis elsewhere ; 

 in the genus Aeolosoma and in the perhaps closely allied Ctenodrllus the under 

 side of the prostomium is ciliated and there are a pair of lateral ciliated pits, 

 possibly of a sensory nature. In the Naidomorpha we meet with the definite sense 

 organs possibly of a tactile nature ; in the genus Slavina there are a series of these 

 ' Sinneshugel,' as VEJDOVSKY has called them, on each segment, the actual arrangement 

 differing with the species ; these elevations consist of specially elongated cells which 

 terminate in fine processes projecting beyond the cuticle. In Lumbriculue the same 

 author has figured ' Becherfb'rmige Organe,' which appear to be very similar ; they are 

 hemispherical elevations of the skin due to the elongation of groups of epidermic cells, 

 which terminate in the same way in fine processes. In Rkynchelmis there are developed, 

 at the breeding season, continuous zones of sense-cells arranged in groups ; the cells 

 have the same elongated form that the sense-cells generally show, and appeal' also 

 to possess the fine processes already mentioned ; VEJDOVSKY believed that he could 

 trace nerves into connexion with these cells. 



VEJDOVSKY and CERFONTAINE have described and figured groups of what appear 

 to be sense- cells in Lumbricus ; these consist of long cells which are so arranged 

 as to project slightly from the general body-surface ; they are furnished at the extremity 

 with fine processes and occur chiefly on the anterior part of the body, often in particular 

 proximity to the setae. Among the exotic earthworms but little is known of sense- 

 organs ; MICHAELSEN has figured and described in Acanthodrilus georgianus a pair 

 of papillae on the tenth segment which would seem to be sense-organs rather than 

 glandular modifications of the epidermis ; they consist of the same kind of elongated 

 cell that is usually associated with sense-organs ; and fine strands, apparently of 

 a nervous nature, could be traced into them ; it is very possible that similar papillae, 

 many of which, indeed most, have not been subjected to microscopic examination in 

 other Acanthodrilides and other earthworms, are sensory in function. 



Eyes are present in a few Naids. They appear to consist of a lens-like body 

 embedded in a cup of pigment ; a strong nerve from the brain supplies each eye. 



In the genus Pontoscolex and also in the nearly allied Onychochaeta there are 

 certain peculiar epidermal structures which may be of a sensory nature; these were 

 first described by PERKIER and have since been described and illustrated by HORST 

 and by myself in the same genus. They consist of a large spherical deeply staining 

 cell imbedded in a large sac which lies at the base of the epidermis ; the cell has 

 a conspicuous nucleus, as is shown in the figures of both PERKIER and HORST. The 



