No. I.] SENSE-ORGAA'S OF LUMBRICUS AGRICOLA. 225 



by way of the epidermal nerves. Retzius ('92) differs from 

 Lenhossek in regard to the central endings of the sensory 

 fibres. He found that these sometimes ended in the same 

 ganglion which they entered, and that their ends were not 

 always tapering, but were "in der Regel etwas knotig-varicos, 

 ungefahr wie bei anderen sehr einfachen Nervenendigungen, 

 gewohnlich etwas gebogen und nicht selten etwas verzweigt." 

 I have not found such endings. Retzius found in each half of 

 the ventral nerve-cord three parallel longitudinal tracts of sen- 

 sory fibres. Of these the outer and largest one received sen- 

 sory fibres entering by all three nerve-roots ; the median bundle 

 was next in size and received fibres from the anterior and 

 median nerve-roots ; while the inner and most delicate tract 

 received fibres only from the median nerve-root. That means 

 that the sense-organs around the median zone of a metamere 

 furnish fibres to all tliree tracts, those around the cephalic part 

 to two, and those around the caudal part to but one. Apathy 

 ('92) believed that the sensory fibres described by Lenhossek 

 and Retzius were not sensory but motor fibres, and were not 

 connected with epidermal cells. 



Distribiilioji of tJic sense-organs. — Leydig ('65) found the 

 sense-organs on both extremities of Lumbricus. Vejdov- 

 sky ('84) extended the distribution over a few metameres back 

 of the head ; Ude ('86) extended it over the whole body, and 

 first noted the median zone of sense-organs. Cerfontaine ('90) 

 added to this the fact that this zone is situated on a crest of 

 the epidermis. His statement that this crest is more promi- 

 nent on the ventral surface has not been confirmed by my 

 observations. No observer has noted the cephalic zone or the 

 nephridial group, nor has any one attempted a systematic study 

 of the distribution of the sense-organs. No notice has been 

 found of the presence of the sense-organs in the buccal cavity. 



Functions of sense-organs. — But little has been written on 

 the functions of these sense-organs. Although Darwin ('82) 

 did not know of their presence, his physiological experiments 

 may aid in determining their function. He found in Lumbri- 

 cus the sense of hearing lacking, the sense of smell feeble, the 

 sense of taste v/ell developed, the ability to perceive light 



