1G 



OLIGOCHAETA 



sac in which the cell in question lies seems to be connected with the surface 

 by a canal ; such a canal is figured by PERKIER, but HORST does not indicate 



Fig- 3- 



EPIDERMAL SENSE CELL 



OF PONTOSCOLEX. 



(After Horst.) 



The cell is in the middle of the 

 figure. 



it distinctly. VEJCOVSKY compared these cells with the large 

 cells in Anachac.ta, which represent the missing setae ; 

 I supported that contention because it appeared to fit in 

 with my view that the ' Perichaetous ' condition is the more 

 primitive, and that these cells were the remains of a Peri- 

 chaetous condition in Pontoscolex; I am not now convinced 

 of the justice of this view which is not shared by HORST ; 

 it seems probable, as he suggests, that the cells are of 

 a sensory nature ; as to the special sense of which they are 

 the organs that is a matter impossible at present to decide ; 

 it is just conceivable that they may be rudimentary eyes ; the central cell appears 

 to be highly refractive and a ray of light would pass through it to the tissue below ; 

 but the entire absence of any pigment layer in connexion with the organs seems to 

 negative the likelihood of that view. In the meantime, the accompanying woodcut 

 expresses the general form of these organs which may be regarded as sense-organs 

 of some kind. I did, but do not, compare them to the 'Pacinian bodies' of Eudrilus, etc. 

 A peculiar form of sense-organ is to be met with in many Eudrilids. These 

 organs were first described by myself in Eudrilus (62) and compared, erroneously 

 as I now think, with the epidermal bodies of Pontoscolex that have just been described. 

 Since then they have been studied by HORST in Eudrilus and by myself in several 



other genera, such as Hyperiodrilus 

 and Heliodrilus. They are somewhat 

 oval bodies, and lie just below the 

 epidermis, though above the circular 

 muscles ; the cells of the epidermis 

 which cover them are shorter than 

 the others and not glandular. These 

 bodies consist (see fig. 4) of a deeply 

 staining granular nucleated cylindri- 

 HYPERIODRILUS. EPIDERMAL SENSE BODY. cal core, round which are apparently 



i. Nerve supplying it. wrapped a series of membranes, also 



nucleated, though with smaller nuclei than the core ; the whole structure reminds 

 one most forcibly of a Pacinian corpuscle. In more than one case I fancied that 

 I could detect a nerve fibre passing from the core, and I have represented one in the 

 accompanying woodcut. There is nothing exactly comparable to these organs in any 



Fig. 4. 



