TUBIFEX. 315 



a number of hairs (6 or 7) surrounding certain of the 

 setae near the apex. He states that they result from the 

 splitting up of the horny substance of the seta. He goes 

 on to describe how a number of small dark particles are 

 placed at intervals along the hairs. It is quite easy to 

 recognise the condition that he describes, but it seems to 

 me that his observations may bear another interpretation. 

 When the worms are kept in the laboratory for a time, 

 even though they are placed under running water, they 

 become infested with fungus growths. These have the 

 form usually of long, delicate filaments which appear to 

 have their origin between the prongs of the setae, and 

 present exactly the appearance described by Lankester. 



THE BODY WALL. 



As in most Oligochaeta the body wall consists of the 

 following layers : — (1) Cuticle, (2) Epidermis, (3) Circular 

 Muscles, (4) Longitudinal Muscles, and (5) Peritoneal 

 Epithelium. 



1. The Cuticle is a delicate layer of non-cellular 

 nature which lies outside the epidermis, and is formed as 

 a secretion from the epidermal cells. It completely 

 invests the body, and is about 3 /* thick. 



2. The Epidermis consists of a single layer of 

 cells throughout, but varying somewhat in thickness in 

 different parts of the body. For purposes of description 

 we may divide the epidermis into : — (a) Ordinary or extra- 

 clitellar epidermis; and (b) Clitellar epidermis. 



(a) Ordinary or Extra-Clitellar Epidermis. The 

 ordinary epidermis consists of two well-marked types of 

 cells, viz., gland cells and columnar supporting cells, and 

 is from 6 (i to 8 // thick. The gland cells are large, 

 somewhat irregular in outline, and with the nucleus, 

 as a rule, situated in the lower half of the cell. The 



