No. I.] SENSE-ORGANS OF LUMBRICUS AGRICOLA. 219 



restate the facts in the above form. All the facts in the fore- 

 going description which have been described by previous in- 

 vestigators have been carefully verified in my own work. In 

 the following critical summary of the literature, I have tried to 

 indicate briefly the facts previously described and also those 

 not before noted. 



Summary of the Literature on the Sensory Structures in the 



Epidermis of Lumbricus. 



The early observers, such as Pontallie ('53), Clark ('57), and 

 Lankester ('65), considered that the upper lip of Lumbricus 

 served as a sense-organ because of its rich nerve supply and 

 its mobility. After the cellular structure of the epidermis had 

 been demonstrated, investigators began to seek an explanation 

 of the well known sensitiveness of Lumbricus by referring it 

 to definite cellular elements of the epidermis. This cellular 

 structure was first perceived by Leydig ('65), who discovered 

 the supporting cells, gland-cells, and sense-organs. 



Gland and s7ippo7'ting cells. — Leydig ('65) considered the 

 gland-cells to be sense-organs having the appearance of uni- 

 cellular glands, because, when isolated, he found an apparent 

 nerve-fibre connected with each. Below the supporting cells 

 of the upper lip, he described and figured, "verastigter 

 Wurzelnerv," which he considered a prolongation from the 

 bases of these cells. Perrier ('74) supported Leydig's observa- 

 tions, although he stated that positive proof was needed as to 

 the character of these apparent nerve-fibres. Mojsisovics ("77) 

 found the same network below the supporting cells. Vejdovsky 

 ('84) considered that these apparent nerve-fibres might be either 

 connective tissue fibre or efferent nerve-fibres passing to the 

 epidermis as to any other organ, and that their presence was 

 no indication of the sensory nature of the common elements of 

 the epidermis. Ude ('8S) considered Leydig's observations on 

 the basal network of the supporting cells probably correct. It 

 seems to me very probable that the fibres attached to the gland- 

 cells were really nerve-fibres, the intraepidermal fibres described 

 in this paper ; these might easily come away with the isolated 



